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_Title:_ The Science of Life; or, Animal and Vegetable Biology
_Date of first publication:_ 1880
_Author:_ J. H. (Joseph Henry) Wythe (1822-1901)
_Date first posted:_ June 2, 2015
_Date last updated:_ June 2, 2015
Faded Page eBook #20150607
This ebook was produced by: Brenda Lewis, Elizabeth S. Oscanyan & the
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Frontispiece:
BIOLOGICAL TYPES.
I.
I PROTOPHYTES
.
II THALLOGENS
.
III ACROGENS
.
IV ENDOGENS
.
V EXOGENS
.
II.
I PROTOZOA
.
II RADIATA
.
III MOLLUSCA
.
IV ARTICULATA
.
V VERTEBRATA
.
THE
SCIENCE OF LIFE;
OR,
ANIMAL AND VEGETABLE BIOLOGY.
BY
REV. J. H. WYTHE, A.M., M.D.,
AUTHOR OF “AGREEMENT OF SCIENCE AND REVELATION,” “THE MICROSCOPIST,” ETC.
* * * * *
NEW YORK:
P H I L L I P S & H U N T.
CINCINNATI:
W A L D E N & S T O W E.
1880.
COPYRIGHT 1880, BY
P H I L L I P S & H U N T ,
NEW YORK.
PREFACE.
This book is written for those who have some elementary knowledge of
Physiology. It gives a general outline of the origin, structure, typical
forms, and functions of living things, so as to serve as an introduction
to the examination of the objects themselves.
Although a text-book must of necessity be a compilation of facts, yet
many years of practical experience with the microscope have enabled the
writer to describe many things with the confidence of personal
observation. Some of the illustrations are original, others have been
selected from Dr. Carpenter’s works on Physiology and the Microscope, T.
R. Jones on Zoology, Lindley’s Botany, Mac Ginley’s Introduction to
Biology, and other standard works.
It has been the aim of the author to guide the student through the
fundamental principles of Biology to the contemplation of the vast
temple of animated nature, with its varied compartments intimately
connected with each other, and with the central one of all, the human
type. In every avenue and chamber and dome of this wondrous edifice the
Christian student recognizes the truth that “POWER BELONGETH UNTO GOD.”
OAKLAND, CAL., _January,_ 1880.
CONTENTS.
I. WHAT IS LIFE? 9
II. LIVING MATTER 26
III. PARENTAGE 40
IV. TISSUE FORMATION 52
V. TYPES OF CONSTRUCTION 72
VI. PROTOPHYTES 84
VII. THALLOGENS 98
VIII. ACROGENS 109
IX. ENDOGENS 122
X. EXOGENS 137
XI. PROTOZOA 161
XII. RADIATA 170
XIII. MOLLUSCA 192
XIV. ARTICULATA 213
XV. VERTEBRATA 239
XVI. THE HUMAN TYPE 281
T H E
S C I E N C E O F L I F E .
* * * * *
CHAPTER I.
W H A T I S L I F E?
Am I but what I seem—mere flesh and blood?
A branching channel, and a mazy flood?
The purple stream that through my vessels glides,
Dull and unconscious flows, like common tides.
The pipes, through which the circling juices stray,
Are not that thinking I, no more than they.
This frame, comparted with transcendent skill,
Of moving joints, obedient to my will,
Nursed from the fruitful glebe, like yonder tree,
Waxes and wastes: I call it _mine_, not _me_.
New matter still the moldering mass sustains,
The mansion changed, the tenant still remains;
And from the fleeting stream, repaired by food,
Distinct, as is the swimmer from the flood.
—ARBUTHNOT.
1. The term Biology, (from the Greek, _bios_, life, and _logos_, a
discourse, or doctrine,) signifies the Science of Life. It includes the
study of all the phenomena of living beings, both animal and vegetable,
in order to discover the general principles which underlie their origin,
formation, varieties, and functions. The special study of structure is
termed Morphology, or Anatomy. The study of functions is Physiology. The
origin, development, and arrangement of the varieties of the vegetable
world make up the study of Botany. Zoology considers the various kinds
of animals. All these sciences, and many others, combine in Biology.
To the Christian student Biology affords a multitude of evidences of
intelligent design, proving the universe to be the product of Supreme
Will. It also contains proof of the reality of spiritual existences, in
addition to physical atoms and physical forces.
2. The cause of difference between the living and the non-living is the
most fundamental question of Biology, and the answers given to this
question by modern writers depend upon the schools of philosophy to
which they are attached.
Much learning and industry have been employed within the past few years
to teach the system of _Monism_, or the theory that all being can be
resolved into a single principle. Among those who entertain this view,
some hold to materialism, or the development of all forms from primitive
atoms. Others are idealists, conceiving matter to be identical with
force. Others again are pantheists, holding that mind is the only
substance, and that the universe is an emanation of the universal mind.
The doctrine of rational _Dualism_, which asserts two real principles of
existence, mind and matter, with their special endowments and forces,
stands in opposition to all forms of Monism whatever.
Since the dawn of history these speculations have divided philosophers,
and learning of all kinds has been used to maintain the views of either
side. Leucippus and Democritus, the masters of Epicurus, taught the
doctrine of invisible and indestructible atoms, with spontaneous motion,
as the cause of all things. Anaxagoras and Plato argued for a regulating
intelligence, producing order, so that “the world’s activities are
reflections of God’s thoughts.” The Hebrew and Christian Scriptures, as
well as all other writings which exhibit the religious beliefs of
mankind, Koran or Shaster, King or Avesta, (the sacred books of
Mohammedans and Hindus, Chinese and Persians,) teach the doctrine of
Dualism, or the distinction between mind and matter.
3. The revival of Monistic philosophy in the last century has awakened
much discussion, and each of the sciences in turn has been made the
arena of conflict. In Biology, Darwin, Spencer, and Hæckel are arrayed
against Agassiz, Lionel Beale, and M’Cosh, and the contest of mind has
brought to notice a wonderful accumulation of facts, sufficient, we
think, to settle the central question of philosophy concerning life.
In the present work the facts of Biology are regarded as confirmatory of
the principles of rational Dualism. In the judgment of the writer there
is no conflict between science and revealed truth, but such complete
agreement that the facts of science can be best understood and explained
in consistency with that philosophy which religion has made prevalent in
the minds of the majority of men. Yet the learning and apparent candor
of many Monistic writers entitle them to respect, even if we fail to
agree with them, and truth, which should be the object of all study, is
not aided by epithets or personal acrimony.
4. Some scientists ignore the question of the cause of life, and confine
themselves to the physical and chemical phenomena associated with living
things; but this is quite unsatisfactory. That there are differences
between the living and the non-living will only be denied by the most
thorough partisans of Monism. These differences depend on something in
the living which is absent from the non-living. In common parlance we
call it life, or life-force. Such a life-force is as necessary to
Biology as gravitation is to Physics, or light to Optics.
Writers who avoid Dualism, or who acknowledge antagonism to it, have not
been able to give a clear definition of life.
_Bichat_ defines life as “the sum of the functions by which death is
resisted.” This is but saying that life and death are opposite states.
_Dr. W. B. Carpenter_, although believing in the difference between mind
and matter, speaks of life as “the condition of a being which exhibits
vital actions;” which is but another mode of stating that life is a
condition or state of living.
_Coleridge_ considered life as synonymous with “individuation.” This is
equivalent to separate existence, and includes metals, and stones, and
all non-living things.
_Herbert Spencer_ defines life as “the continuous adjustment of internal
relations to external relations.” This definition will apply to a
boiling tea-kettle, a steam-engine, or a burning candle, as well as to a
living thing.
_Haeckel_ declares “that all natural bodies which are known to us are
equally animated, and that the distinction which has been made between
animate and inanimate bodies does not exist.” This exceedingly bold and
strange statement is rendered necessary by the logical demands of the
Monistic philosophy. In a subsequent place we shall examine particularly
the differences between animate and inanimate bodies. (See Chap. II.)
All such definitions and statements evade the real question: that is,
What makes the difference between a living body and the same body a
moment after death?
5. The cause of life is a mystery only to the materialist. To the
Christian philosopher it is as plainly revealed as any other fact of
nature. The Bible asserts that life results from the union of a
spiritual nature with the material body. In other words, life is the
influence resulting from the union of matter and spirit; and this
dualistic theory is the only one which suffices to explain the phenomena
of living things.
Moses declares of man that God “breathed into his nostrils the breath of
life; and man became a living soul.” In accordance with this view death
is everywhere referred to in Scripture as a departure of the spirit. The
medical evangelist, St. Luke, when describing the resuscitation of
Jairus’ daughter, says, “Her spirit came again, and she arose
straightway.” St. Paul describes the body as a tent, or house, in which
the spirit may be present or absent. It is also remarkable that the same
Hebrew word which describes man as a “living soul” is applied to animals
in the same history of creation. Gen. i, 20, 30. They also are living
souls.
This view of the cause of life was also held by ancient Grecian
philosophy. Aristotle attributed organization and vital actions to a
series of _animating principles_, (_psychai_,) different in each
organized body, and acting by power derived from the supreme animating
principle, (_physis_.)
Müller, the father of modern physiology, substituted the term “_organic
force_” for that of “animating principle,” and Dr. Prout used the term
“organic agent.” The precise term employed is of but secondary
importance compared with the dualistic conception, which is quite
satisfactory to the large majority of thinkers.
6. We shall be able to appreciate this subject better if we consider the
life-history of some simple animal.
It is well known that infusions of vegetable or animal substances
contain many living forms of extreme simplicity of structure, called
_Infusoria_. Many such are found in ponds, or running water, or in the
sea. A very beautiful kind of Infusoria, common among half-decayed
leaves, has received the name of Vorticella, or bell-shaped animalcule.
There are several species, the most common being known as _Vorticella
nebulifera_. Take up from a pond a little twig, covered with mold or
mucus-like substance, and place it under the microscope. In all
probability you will see a colony of Vorticellæ, (Fig. 1.)
Each animalcule has a glassy, transparent bell, with a thick lip or rim,
fringed with cilia or hair-like projections. These cilia are sometimes
withdrawn, but when active vibrate rapidly, so as to make a sort of
whirlpool in the water, in the vortex of which smaller animals or
vegetables may be conveyed as food to the interior of the Vorticella. A
number of pellucid spots may be seen in the body of each animalcule,
which were formerly regarded as stomachs. Professor Ehrenberg, who
elaborately investigated this class of animal life, gave the name
_Polygastrica_ (many stomachs) to those animalcules which presented this
appearance. By feeding with coloring matter, as carmine or indigo, these
stomachs have been found to be merely excavations in the bioplasm, or
living matter, which constitutes the body of the animal. Some of these
excavations are extemporaneous, but one cavity is persistent, and
pulsates in a peculiar manner, so that it has received the name of
_contractile vesicle_. Each glassy bell is attached to the twig by a
slender thread, and usually swings to and fro in the water with the
thread or footstalk fully stretched, and the cilia moving rapidly.
Frequently, however, and especially on some unusual jar, or other cause
of alarm, the thread contracts in the form of a spiral, and the cilia
are withdrawn into the substance of the bell.
[Illustration: FIG. 1.—_a._ Colony of Vorticella. _b._ _b._ _b._ Stages
of fission, or self-division. _c._ A separate individual. _d._ Encysted
state. _e._ Ruptured cyst emitting gemmules in a mass of gelatine or
gum. _f._ Acineta parasites.]
These Infusoria usually increase by self-division. The globular bell
becomes first flattened, then notched, and lastly divided. As soon as
division takes place there are distinct motions in the separate
individuals. In one of them the cilia are absorbed, and new cilia appear
on the side next to the footstalk. The motions of the new cilia form a
current sufficient to detach the newly-formed bell, which becomes
isolated, swims away, and develops a new stalk, after fixing itself in a
new place.
Another mode of increase sometimes occurs, in which the animalcule seems
to pass through a sort of chrysalis state. It becomes encysted, like the
primitive forms of vegetables. It is first rounded, then a sort of
gelatinous secretion hardens into a case, protecting the interior from
antagonizing cold, etc.; then the encysted body breaks up into nuclei,
or separate spots, and afterward into numerous gemmules, or small germs,
which are set free by the bursting of the envelope, and swim away to
grow into new individuals.
During the encysting process the Vorticella often appears like a
globular pincushion with pins sticking in it. This is now known to be
caused by a parasite, the _Acineta_, which sends forth a projecting arm
into the body of its host to absorb its fluid nutriment.
7. I have selected the Vorticella for a first lesson on Biology because
it is quite common, and simple enough for study. What can we learn here
of life-force? Is there such a thing as life-force? Is there a
difference between the living Vorticella and the dead twig it rests
upon? Some philosophers, as we have seen, declare that there is no
difference. The old astrologers used to say that all things were living,
and the teachers of ancient magic and heathen philosophy taught a
universal world-spirit, which is the life of all things. To this
pantheistic theory the adherents of the dogma of the mechanical origin
of the universe naturally gravitate. It is more consistent with common
sense and true philosophy, as well as with the facts of science, to
maintain an essential difference between the animate and the inanimate.
Can the dead twig move spontaneously, like the living animalcule? Does
it assimilate food and reproduce itself like the Vorticella? Or can a
dead animal respond to natural stimuli like the living? Not a single
fact has been brought forward to prove the identity of the living and
the non-living. It is at best only a theory. “On the other hand,” says
Dr. Beale, “thanks to the steady progress of minute investigation,
unnoticed by popular writers, and perhaps unknown to them, the
conclusion that life of every kind is distinct from ordinary forces is
at this time more strongly supported by facts, and more firmly
established than it ever was.”[1]
8. In order to defend the Monistic philosophy, and the identity of
animate and inanimate objects, some argue that matter has no existence
as such, but that each atom is only a center of force. They thus
repudiate the charge of materialism, since they teach that every thing
is spirit. This is a most subtle and ingenious method of defense, yet is
just as baseless as the grosser Monism, which considers all to be
material. Newton’s law, of gravity being in direct ratio to the mass of
matter, that is, to the number of atoms in the mass, proves atoms to be
real physical existences. All chemical science is based on the doctrine
that atoms and molecules have weight, definite proportions or relations,
and hence definite form. The law of Avogadro and Ampere, as it is
called, that “equal volumes of all substances when in the state of gas,
and under like conditions, contain the same number of molecules,” is
confirmed by all chemical experiments, and necessarily implies the
reality of atoms and molecules. Our own consciousness of matter, also,
the sense of otherness which pertains to our knowledge of the objects of
sense, is as reliable as any other knowledge. We know the _otherness_,
as well as the weight and inertia of matter by the same faculties by
which we know that two and two make four, and not five. The obvious
distinctions between the living and the not living are all proofs of
Dualism.
9. As to the theory that atoms have a physical and a spiritual side, by
which opposite qualities are exhibited, it carries its own refutation,
since it is plainly impossible for a healthy mind to believe that
contrary properties can inhere in any thing at the same time. Mr. Joseph
Cook has pertinently said: “If matter is a double-faced unity, having a
spiritual and a physical side, there must co-inhere in one and the same
substratum extension and the absence of extension, inertia and the
absence of inertia, color and the absence of color, form and the absence
of form. To assert that these fundamentally antagonistic qualities of
matter and mind not only inhere, but co-inhere, in one and the same
substratum, is to assert that a thing can be and not be at the same time
and in the same sense. This limitless self-contradiction wrecks in this
age, as it has wrecked in every age, the pretense that there is but one
substance in the universe.[2]
10. The continuance of life in an organism composed of new atoms, after
the old atoms have been cast off, proves that the cause of life does not
spring from the atoms themselves. An atom of oxygen or hydrogen, endowed
with life to-day, as part of an organized molecule of a Vorticella, or
as part of our own bodies, may be to-morrow released from its vital
connections, and be transported, as water or air, to remote parts of the
globe. It may form part of the gigantic Sequoias of the Sierras, the
Cinchona-trees of the Andes, or the Rhododendrons of the Himalayas.
Before the death of the original organism, or the tree it next served,
that atom of oxygen or hydrogen may be again discarded, and pass into
the germ-cell of an animal, or become part of one of the tissues of a
man in a distant part of the world. It is evident that _that_ atom did
not produce the life with which it was first associated. What may happen
to one atom may happen to all the atoms of an organism. In active living
beings this actually does happen, so that all the atoms of a living body
become disconnected, and return to the inorganic world, or go to serve
other organisms, while other atoms take their places, yet the organized
body lives on. Its life depends not on the new atoms, for the body was
animate before these atoms came; nor does it depend on the old atoms,
for it continues after they have gone. It must, therefore, depend upon
something different from the material atoms. As matter and spirit are
the only objects of thought possible to us, and as life does not depend
on matter, it must depend on spirit. If existence and activity continue
after the removal of the original matter, as we have seen, they may also
continue after all matter is removed. Continued spiritual existence is
certainly conceivable, and in view of the endowment of new atoms by the
vitalizing force, we must admit it to be probable, even after the
material of the organism is all destroyed.
The cause of life is more than matter and physical force. It uses both
matter and force for its own ends and after its own laws. “Its power of
control over matter and physical laws proves its superiority over, and
its distinction from, matter. Life is matter’s master, not its slave.
Life is a workman, a builder, a chemist; and each organized being has
its own appropriate life, the result of the union of the spiritual and
the material in itself.”[3]
11. The view we have taken of the difference between the animate and the
inanimate objects of creation is one which is growing in favor with the
principal workers in biological science. Dr. Beale’s discoveries and
generalizations in Histology have done much to arrest the skeptical
tendencies of scientists, and in one of Mr. Huxley’s latest utterances
he acknowledges that “the properties of living matter distinguish it
absolutely from all other kinds of things,” and that “the present state
of knowledge furnishes us with no link between the living and the
not-living.”[4] The last-named anatomist names the distinctive
properties of living matter as follows: 1. Its chemical composition; 2.
Its universal disintegration and waste by oxidation, and its concomitant
reintegration by the intussusception of new matter; 3. Its tendency to
undergo cyclical changes.
Dr. Beale shows that “no relation can be established between the
chemical or other material properties of different kinds of living
matter that will in any way account for the different results as regards
development and formation. The different powers or properties of the
particles cannot be due to difference of chemical composition. All
living particles consist of comparatively few elements, and no
differences in the proportions of these would enable us to explain the
different results of the act of living.
“This wonderful stuff, which is the first state of every thing that has
life, splits up when it is destroyed into a few chemical compounds, from
the study of which, however, chemists have hitherto failed to arrive at
any conclusion as regards the atomic relations of the component elements
of the matter during life. Neither, as far as has been ascertained, is
there any constant relation between the volume, or kind, or aggregation
of the matter which is the seat of the manifestation of the vital power
and the form of living being that is to be evolved from it. Man’s matter
is no more elaborate, no more complex, no more beautiful, than dog’s
matter or sheep’s matter; but it is in the _power_, not in the matter,
that we must look for the cause of the remarkable difference of the
results. Insignificantly in matter, but transcendently in power, does
the man-germ differ from the dog-germ. Wonderfully different power may
be transmitted by particles of matter that resemble one another in every
particular that can be ascertained.” Again: “It is by the transmission
of power to matter, rather than by the bodily transference of millions
of particles of matter having particular properties and detached from
matter having similar properties, that inheritable peculiarities are
handed down from parent to offspring. And it must be borne in mind that
structure-forming capacity, which is not even rendered evident until
forty or fifty years shall have passed since the original germ-speck
originated in the parent, may affect pounds weight of matter, not one
grain of which will be acquired until long after every atom of that
primitive speck shall have ceased to live and have been removed from the
organism. Matter, with its forces, continually comes and goes, while
power only remains unimpaired and preserves its identity. Power has been
handed down—has been transferred from old particles to new particles of
matter; but the original matter—nay, in the case of some of the largest
animals, hundreds weight of matter—must have come and gone, while the
original power remained.” “Vital power works according to predetermined
order, and the results of its working are seen in different
consequences, at different periods of its action.” “Vital power prepares
for far-off events, and acts as if phenomena, not to occur until after
the lapse of a considerable time, had been from the first foreseen.
Vital power suspends the action of chemical affinity, and piles material
particle above particle, the force of gravity notwithstanding.”[5]
12. Sometimes life remains _dormant_ from lack of appropriate stimuli,
or conditions, or from some unexplained peculiarity. This proves those
philosophers to be in error who imagine that molecular change is
essential to life. The seed which has been held in the hand of an
Egyptian mummy perhaps for thousands of years, retains the vital power,
and may sprout under favorable conditions. The wheel animalcule
(Rotatoria) has been dried and resuscitated many times in succession,
and Messrs. Drysdale and Dollinger have proved that the germs of
Infusoria cannot be destroyed by the heat of boiling water, but live
when the thermometer shows a heat of 300° F. These resisting germs,
floating in the air, will soon revive on the accession of moisture.
13. _Death_ occurs when the cause of life is removed. Life is not
synonymous with spirit, but is peculiar spiritual influence on matter;
the result of the union of created spirits and elemental matter. When
the spiritual essence ceases to act upon the matter of the organism we
say the body is dead, and then disintegration and chemical decomposition
succeed. There is a two-fold death—the death of the organism as a
whole, called somatic, or bodily death, and molecular death, or the loss
of vital activity in the molecules of the body. Life begins in a single
molecule of bioplasm, and is propagated as a force more or less modified
from molecule to molecule, or from cell to cell, as flame proceeds from
one combustible substance to another, or as magnetism is disseminated by
the action of a single magnet through one bar of steel after another.
Molecular death is a continual phenomenon of life during its activity.
It is arrested in dormant life, and is far from being so constant an
attendant upon all the actions of the body as some have taught, yet it
goes on with great rapidity and uniformity. The bioplasts, or living
particles, of each tissue in the body are changed into formed material,
and then pass into decay, while other bioplasts take their places and
keep up the active dance of life. When the spiritual cause, or origin,
of vital phenomena is removed, the molecular activities of the body do
not all cease at once, but gradually. Hair will continue to grow on a
corpse, and the secretion of rattle-snake poison, or of other glands,
continues for a short time after death. Indeed, the circulation of blood
has been witnessed in a section of mouse’s kidney some time after it had
been removed from the body. Yet, uninfluenced by the energizing spirit,
the vital activities gradually cease, and decomposition ensues.
14. To return to our example from the Infusoria, the life-history of the
Vorticella demonstrates both the spiritual origin of life and the work
of a Supreme Intelligence. The evidence of design in its construction is
quite apparent. The extensile threads and vibsatile cilia have, plainly
enough, an object. They subserve prehension of food and the preservation
of existence. Even the contractile vesicle, whose exact purpose we do
not know, impresses our minds with the fact that it serves some purpose.
This design is connected with something different from the material
atoms of the organism, but which controls those atoms, since there is
foresight of future changes, and provision for future changes in the
life-history which will occur after the removal of all the present
material. The self-division of the Vorticella, the formation of new
cilia, the preparation for increase by the encysted form, the division
into nuclei and gemmules, are all examples of this, analogous to the
formation of new structures in the higher animals. The power to produce
these changes is not material but spiritual.
15. Thus our first lesson in Biology brings us to the confines of a
spiritual world. We look across the gulf which philosophy and science
cannot bridge over except by revealed truth, but the telescope of faith
can see realities on the other side as numerous, as diversified, and as
true as the objects of sense which can be weighed and measured by our
physical instruments. We see also the care and providence of a Supreme
Creator. Astronomy adds emphasis to the Psalmist’s declaration, “The
heavens declare the glory of God; and the firmament showeth his
handy-work.” And Biology indorses the sentiments of his eloquent
utterances respecting living creatures: “O Lord, how manifold are thy
works! in wisdom hast thou made them all: the earth is full of thy
riches. So is this great and wide sea, wherein are things creeping
innumerable, both small and great beasts. There go the ships: there is
that leviathan, whom thou hast made to play therein. These all wait upon
thee; that thou mayest give them their meat in due season. That thou
givest them they gather: thou openest thine hand, they are filled with
good. Thou hidest thy face, they are troubled: thou takest away their
breath, they die, and return to their dust. Thou sendest forth thy
spirit, they are created: and thou renewest the face of the earth. The
glory of the Lord shall endure forever: the Lord shall rejoice in his
works.”
CHAPTER II.
L I V I N G M A T T E R .
You may bury me as you choose, if you can only catch me. But you
will not understand me when I tell you that I, Socrates, who am
now speaking, shall not remain with you after having drunk the
poison, but shall depart to some of the enjoyments of the blest.
You must not talk about burying or burning Socrates, as if I
were suffering some terrible operation. Such language is
inauspicious and depressing to our minds. Keep up your courage,
and talk only of burying the body of Socrates; conduct the
burial as you think best and most decent.—PLATO’S _Phædo_.
1. THE only unexceptionable characteristic of living bodies is the
possession of living tissue, or _bioplasm_. This may be present alone,
as in the simple animal and vegetable forms, or it may exist in
association with structure which has been formed by it, and hence called
_formed material_. The bioplasm is nourished by _pabulum_ which is
generally furnished in fluid form.
[Illustration: FIG. 2.—Amœba princeps × 150. In various shapes.]
2. The old division of bodies into organized and unorganized—the former
having organs, or distinct parts, with definite structure, and of
special use—is no longer applicable, since there are some living things
which have no organs. The _Amœba princeps_, Fig. 2, one of the most
elementary animal forms, is composed of a jelly-like homogeneous
bioplasm, capable of indefinite extensibility and of indefinite use. It
is so constantly altering its outline that it does not retain the same
shape for two successive minutes. It obtains its food by flowing around
it, and digests by direct absorption.
3. Of such simplicity of structure are all the primitive forms of
vegetable and of animal life, while in bone, cartilage, flesh, skin, or
any other structure of the higher animals, we find such simple,
jelly-like, living matter, or bioplasm, similar in appearance to the
Amœba, scattered in minute particles all through the tissue, and careful
observation will show how this living matter is transformed into the
formed material of the several tissues.
4. All animals and vegetables have originated from minute particles of
such bioplasm. Every dog, horse, man, whale, jelly-fish, oak, cedar,
grass, sea-weed, etc., began its existence as a particle of bioplasm.
And every tissue and organ, no matter what its form or function, was
built up by similar living matter.
5. In the lowest type of animal life (the Rhizopods) the vital
operations are carried on without any special organs, as we have seen in
the Amœba; a little particle of jelly-like bioplasm, changing itself
into a variety of forms, laying hold of food without members, swallowing
it without a mouth, digesting it without a stomach, moving without
muscles, while the mere separation of a fragment of this jelly, however
small, is sufficient to originate another and independent living
creature, retaining, or rather repeating, all the characteristic
endowments of the original mass. In the higher animals, although the
first bioplasmic particle subdivides itself into an aggregation of
similar particles or cells, yet there soon appears a structural
differentiation of organs for special uses, which is more elaborate and
heterogeneous as the type approaches the human structure. A single cell
or living particle, however, in any structure is, to all intents and
purposes, a living thing, and possesses powers of assimilation, growth,
and reproduction, altogether different from the mineral or non-living
body.
6. Living matter, or bioplasm, may be considered physically as a
peculiar compound of the chemical elements—carbon, oxygen, nitrogen,
and hydrogen, called by Mulder _Proteine_, and by Mr. Huxley and the
German histologists _Protoplasm_, or the physical basis of life. It is
nearly identical with Albumen. So far as is known, this combination of
elements is always the product of pre-existing, living matter. It has
never been produced in the laboratory, and if it were possible for a
chemist to manufacture albuminoid matter, or protoplasm, it would be
dead protoplasm, and not bioplasm, and would be destitute of vital
properties. Other conditions are necessary to vital phenomena besides
combination of material elements. Light, heat, electricity, and moisture
are all necessary conditions; nor these alone, for with all these
existing and active, the protoplasm may not live. Some other factor is
essential to life besides matter and physical force, as we said in the
last chapter. The term _bioplasm_ is well applied to express matter in
its living state, while _protoplasm_ should be restricted to the
material itself.
7. The essential phenomena of living matter next claim our attention;
or, What can a living thing do which the non-living cannot?
1.) All living things have _spontaneous motion_. The non-living are
passive, and only move by the compelling agency of some external force,
but the force which moves living matter is a force which is inherent,
and cannot be explained by physical laws. Living matter has primary
energy, and can overcome inertia, but the non-living are unable to
originate motion. The spontaneous motions of bioplasm, or living matter,
are molecular, amœboid, or wandering.
_a._ Molecular movement. This must not be confounded with what has been
called Brunonian motion, from Dr. Robert Brown, who first described it
in 1827. The latter is a sort of vibration in small particles suspended
in fluid, and is supposed to be caused by currents formed by heat or
evaporation. In the molecular movements of bioplasm each particle of the
mass seems to be independent of the rest. As the passengers in a crowded
street may go the full length of the street, or turn back, or stop and
double as many times as they wish, so do the particles move in the mass
of bioplasm. Up, down, across, backward, and in all directions—even
through each other—do these molecules move, each impelled by its own
inherent energy.[6]
_b._ Amœboid movement receives this name from its resemblance to the
notions of the Amœba, described in the present chapter, Sec. 2. The
shape is continually changing, by a portion of the body being projected
from the mass, or retracted, or altered in form.
_c._ Wandering movement is a modification of the latter form. A portion
of the bioplasm is projected forward, and along this temporary arm, or
bridge, the semi-fluid molecules flow along, and accumulate at the
farthest end. In this manner the white cells of blood, which are
particles of bioplasm, wander out of the vessels, perhaps by means of
stomata, or holes, in the sides of the vessels, into those tissues of
the body where they are needed, Fig. 3. These motions are wholly unlike
any which occur in lifeless material.
[Illustration: FIG. 3.—Clot of Frog’s Blood, with Migrating White
Blood-cells.]
2.) Another essential property of bioplasm is _growth_. The term growth
does not mean accretion or addition of material, nor increase of size. A
piece of chalk, or a bank of mud, or any non-living thing, may increase
in size by additions to its material. Growth in a living thing is
different. It is enlargement by nutrition, and depends on inherent
motion. In Chap. I, Sec. 13, it was stated that hair would grow on a
corpse, but the term grow was used in a popular, and not scientific,
sense. Hair is not a living part of the body. Hair or nails may be cut
or destroyed without sensation or impairment of the body. They consist
of scales of formed material, pushed forward by the growth of bioplasm
behind them. If you pull out a hair or nail, you reach the quick—that
is, the living or sensitive part. We thus see that some parts of our
body are alive, and others in a non-living state. The formed portions
never grow, but the bioplasm, or living matter, grows. The growth of
living matter is by appropriation and transformation. Bioplasm “alone,
of all matter in the world, moves toward lifeless matter, incorporates
it with itself, and communicates to it, in some way we do not in the
least understand, its own transcendentally wonderful properties.” This
motion and incorporation and endowment constitute growth.
“The rootlets of the plant extend themselves into the soil because the
living matter at their extremities moves onward from the point already
reached. The tree grows upward against gravity by virtue of the same
living power of bioplasm. In every bud portions of this living matter
tend to move away from the spot where they were produced, and stretch
upward and onward in advance. No tissue of any living animal could be
formed unless the portions of bioplasm moved away from one another.”[7]
3.) Living matter has also the power of nutrition, or assimilation by
selection. As this is connected with growth, we might have considered it
under that head, but since writers of the mechanical or materialistic
school attempt to account for it on physical or chemical principles, we
deem it best to examine it separately.
The non-living always enlarges by accretion from similar material; the
living tissue takes into its interior material which it transforms out
of pabulum, which is foreign to its own structure, while at the same
time it discards such molecules or atoms as are unfit for further use.
The chemical composition of the various tissues of the body cannot be
found in the blood, or pabulum, which nourishes the tissues, but results
from metamorphosis, or transformation, by means of the bioplasts.
Endosmose, or the physical property by which fluids pass through
membranes, or gummy matters, will not account for it, since in the
latter there is no change of material, while in nutrition there is
rearrangement of the atoms in the tissue-molecules.
Nutrition has sometimes been compared with crystallization, but
crystallization is a deposit of material from a solution of similar
substance, and is altogether different from nutrition by transformation
and selection.
Nutrition has also been compared with a chemical phenomenon called
catalysis. In this, chemical change takes place because of the presence
of a substance which remains itself unaffected, as when spongy platinum
induces the combination of oxygen and hydrogen gases. In catalysis the
third substance neither gives nor takes from the excited body, but in
nutrition the living matter itself selects appropriate chemical elements
from its pabulum, dissolving their former affinities, and recombining
them in a manner which no non-living substance can do. There is no third
substance present which is known to us, and all the phenomena are
peculiar to living matter, or bioplasm.
4.) Bioplasm can also transmit vital power to its progeny. This property
will be considered more in detail in the next chapter, on Parentage.
8. The peculiar relations and changes of the chemical elements in
bioplasm prove it to possess some power different from not-living
matter, whose actions or results no chemistry can predict. We have said
that bioplasm consists chemically of oxygen, hydrogen, carbon, and
nitrogen. Other unessential elements may also be present in some cases.
But we cannot tell how these elements are combined, if, indeed, they are
combined at all in the proper sense of that word. As all bioplasm
presents the same appearance, although differently formed material
results from its transformation—different in physical properties and in
chemical composition—as muscle, nerve, bone, etc., it is probable that
the elements do not combine at all as in inorganic matter, but that the
ordinary affinities are suspended or modified by vitality.
Bioplasm is a semi-fluid substance, yet it will not freeze at 32° F., as
water does, showing that in this respect it is different from water.
Bioplasm is in a state of constant molecular change, or unstable
equilibrium, since it is constantly receiving pabulum and transforming
itself into formed material, so that it is doubtful if chemical
combination is possible during life, the atomic activities being too
transitory for combination.
When change takes place from bioplasm into formed material combination
occurs, but the formed material is not living tissue, or bioplasm. The
life is gone. It is dead, as if it had never formed part of an organism,
although it may have acquired special properties, as the elasticity of
muscle, or the conducting power of nerve tissue.
If the change referred to occurs suddenly, that is, if the life of
bioplasm is suddenly destroyed, the result is water, albumen, fat, and
sometimes fibrin, and certain salts, as chloride of sodium, etc.
In slower transformations, which are equivalent to slow molecular death,
different materials result, as fat, sugar, milk, biliary acids, etc.
Free oxygen is sometimes absorbed, and very complex compounds result,
often baffling analysis.
Physiological Chemistry has traced many of the results of changes in
formed material, but the composition and physical surroundings of
germinal or living matter will not indicate the nature of its
transformations nor its function. No one can tell whether a particular
bioplast belongs to a vegetable or an animal, whether it will form an
eye or a finger, a nerve or a piece of bone, nor whether its function
shall be secretive, excretive, elastic, or conductive. Nothing but
observation can tell its future life-history.
9. Although all bioplasm has powers or endowments which transcend all
physics and chemistry, and which can only be accounted for by that
dualistic philosophy which acknowledges the reality of both matter and
spirit, yet “all flesh is not the same flesh.” There is an original and
essential distinction between bioplasts. The bioplasm of a fungus never
produces a fish, nor that of a butterfly a man. This will be fully
discussed in the chapter on Parentage. Yet it is no easy task to
discriminate between living forms, especially in what are called the
lower orders. It is difficult to distinguish in all cases between
animals and plants. In the simpler kinds the characters touch and
dissolve into each other, so that no exclusive definition is possible.
Some naturalists think that there are organisms which at one period of
life are vegetable, and at another animal.
10. If we consider their origin, both animals and plants begin life as a
small particle of bioplasm. In plants this forms an ovule, with wall of
cellulose, and in animals it becomes an ovum, or egg, with wall of
albuminous matter.
[Illustration: FIG. 4.—Sertularia Operculata.]
11. As to form, we have no means of separating animals and plants. The
zoospores of Algæ are like Infusoria. Sea-mat (Flustra) and Sea-moss
(Fig. 4) (Polyzoa) are like Sea-weeds, (Algæ,) Corals and Actiniæ are
like flowers.
12. In chemical composition, as a rule, plants are destitute of, and
animals are largely supplied with nitrogen. Yet there are some animal
structures without nitrogen, and some vegetable structures with it.
Cellulose, (woody fiber,) generally found in vegetables, is wanting in
the Fungi, and is found in the covering of Ascidians, (Sea-squirts.)
Starch, under the name of Glycogen, is found in the liver and in the
brain. Chlorophyll, which makes the leaves of vegetables green, is found
among animals, as in Stentor, (the trumpet-shaped animalcule,) and in
Hydra viridis, (the green hydra.)
13. As to locomotive power, bioplasm is essentially active, as I have
described, both in plants and animals. The zoospores of Algæ are covered
with cilia, and move in water like animalcules. Motion is common among
Diatoms, Desmids, Oscillatoria, and other classes of plants, while
Sponges, Corals, Oysters, and Barnacles are largely destitute of
locomotive power.
14. With respect to food, plants live generally on mineral or inorganic
matter, chiefly water, carbonic acid, and ammonia, while animals require
ready-made organic compounds to support life. Thus plants manufacture
and animals consume organic pabulum. Yet Fungi, which are generally
classed with vegetables, feed as animals on organic matters, and
insectivorous plants, as Darwin has shown, feed on animals.
15. Animals generally possess sensation, consciousness, and volition,
yet there is a kind of sensation in the sensitive plant, Venus’
fly-trap, etc., and something like volition in zoospores, or they would
often collide in the active dance they keep up. Plants need rest as well
as animals. Both have their epidemics, poisons, and remedies.
16. If we admit a dualism, or spiritual cause of life, in vegetables, as
well as in animals, it does not prove them immortal. Immateriality does
not imply immortality. Existence, spiritual or material, depends on the
will of the Creator, and we can only know the future as he has revealed
it.
“Heaven from all creatures hides the book of Fate,
All save the page revealed—the present state.”
17. Our study thus far impresses us not only with the truth that all
living things manifest a dualism, but also that all living are
intimately related. Not that all come from a single germ, or from a few
germs, but that animals and plants form, after some sort, a common
family. From the great Father and Fountain of life all living things
proceed, and their existence and endowments are according to his will.
Immaterial, or spiritual existences weave for themselves a beautiful
garment from the inorganic world. The plant bioplasm appropriates
mineral matter, with carbonic acid, water, and ammonia, and by a
wonderful vital chemistry transforms it into organic compounds, as
starch, sugar, gum, albumen, etc. These compounds afford pabulum to
animal bioplasm, and are transformed to blood, muscle, nerve, and other
complex animal substances. After these transformed products have served
the purposes of animal life they are discarded, and return again to the
mineral world. Thus the wonderful wheel of life revolves from age to age
under the watchful care of divine Providence.
18. The intimate relations of living things may find a mathematical
illustration in the logarithmic spiral, such as is described by a ship
sailing N. E. at an angle of 60° from the pole. It is the _spira
mirabilis_ of Jas. Bernouilli, who desired one to be engraved on his
tomb, with the motto: “_Eadem mutata resurgo_”—”I rise the same, though
changed.” It is a spiral which has the same character in all its parts,
and which may continually decrease in the size of its windings without
coming to a point, or increase the number of its convolutions to
infinity. Such a spiral may illustrate the continuity, yet varying
amplitude, of creation. We may trace the progressive windings of
creative power from the motions of inorganic bodies in space to the
motions of bioplasm in the vegetable world and to the higher
nerve-structures of animal life. In all organic matter we see the
workmanship of the same Great Artist:
“Lo! on each seed within its slender rind
Life’s golden threads in endless circles wind;
Maze within maze the lucid webs are rolled,
And, as they burst, the living flame unfold.”
In exact truth, however, each widening circle of creation exhibits some
new and higher form of creative power and skill. The circle widens, and
is also in another plane. Something has pushed forward the center. Every
spiral requires a progressive force, as well as a centripetal and
centrifugal one. Each specialization—either elevation of type or
specific difference—involves new force-expenditure. Certain factors
have been successively added. First, we find inorganic matter, of many
kinds, or of a single kind. Next, the physical forces, so-called, but
really the activity of a personal Creator on the matter he has formed.
Then we find life, or the activities in matter of created spirits in
most wonderful gradation. Rising to another plane we find added to this
life mind-force, or intelligence. Still higher we find spirit, properly
so-called, possessed with moral properties, giving dignity to men and
angels. Yet the spiral is not broken, it is but expanded, and the
analogies and relations have a distinctive similarity, since they are
equally the work of one God and Creator of all. As the physical forces,
by attraction and vibration, and conservation, arrange the cosmos, or
physical universe, so the various bioplasts weave the living tissues for
the living creature—the microcosmos—and so the conscious acts of our
spirits weave the character of our future life.
CHAPTER III.
P A R E N T A G E .
We must get rid of all these complications of an erring
philosophy, this floating chaos of mist and phantasms, and
return to the Natural Realism, which all men have been learning
from their first hours of childhood, and can never unlearn,
before a science of Physics can be really founded. Its first
principle is that we are real persons, living amid a real world
of material objects distinct from ourselves. And this double
truth leads upward to One who is the cause both of matter and
mind, the Supreme Reality, who dwells in light inaccessible, but
who can reveal himself, and has revealed himself, in love and
mercy to the souls he has made. —_Modern Physical Fatalism_, by
T. R. BIRKS.
1. Two theories divide the learned world respecting the genesis of
living things; the doctrine of parentage, or the descent from living
creatures each created “after his kind,” and the theory of spontaneous
generation of the living from the non-living, and the transmutation of
one kind of living beings into another. The first theory is sometimes
called the doctrine of Creation, the latter that of Evolution.
2. The word Evolution simply means _to unfold_, and may be used to
express the life-history of individuals or of species, or the
development of the plans of the Creator in the natural world. To such a
meaning there would be no objection by any one, but as it is generally
understood to mean the mechanical or monistic view of the universe,
which ignores a Creator, and teaches the eternity of substance, the
invariability of law, and the transmutation of living beings, its use
should be restricted to that view. Any other application of it leads to
confusion of thought.
3. There is nothing new in the modern doctrine of Evolution. Among the
Greeks, Leucippus, Democritus, and Epicurus taught that all forms and
phenomena came from the spontaneous motions of atoms, and this view, in
all probability, was a product of older Indian pantheism.
Modern upholders of transmutation differ from each other greatly in the
details of the theory. Some are atheistic, or agnostic, leaving the
Creator entirely out of view. Among these, some teach, like Lamark, the
self-elevation of species by appetency, or desire, use, and effort.
Others, as Darwin, Haeckel, and many late writers, teach what is called
natural selection with spontaneous variability, or the survival of the
fittest. Others again, as Draper and Spencer, teach modification of
species by the surrounding conditions. Some evolutionists are deistic,
like Owen and Mivart, and teach a pre-ordained succession, under
internal force or innate tendency; or, as Morell and Murphy argue,
evolution by unconscious intelligence. In opposition to these views the
majority of naturalists of this and the past age hold to the doctrine of
parentage, and deny the change or transmutation of species, although
admitting a certain amount of physical variability, producing races or
varieties. Among these may be named Linnæus, Cuvier, Agassiz, Dana,
Guyot, M’Cosh, Balfour, Dawson, Milne, Edwards, and Seelye.
4. The acknowledged ability of Agassiz in regard to all matters
connected with natural science entitle his opinions to careful
consideration. He says: “It is my opinion that naturalists are chasing a
phantom, in their search after some material gradation among created
beings, by which the whole Animal Kingdom may have been derived by
successive development from a single germ, or from a few germs. . . . It
is contradicted by the facts of Embryology and Palæontology, the former
showing us norms of development as distinct and persistent for each
group as are the fossil types of each period revealed to us by the
latter.” “If they are linked together as a connected series, then the
lowest Acaleph should stand next in structure above the highest Polyp;
and the lowest Echinoderm next above the highest Acaleph. So far from
this being the case, there are, on the contrary, many Acalephs which, in
their specialization, are unquestionably lower in the scale of life than
some Polyps, while there are some Echinoderms lower in the same sense
than many Acalephs.” He shows that the same principle applies to classes
in other types: “There are some members of the higher classes that are
inferior in organization to some members of the lower classes.” The same
thing is true in Embryology: “A Vertebrate never resembles at any stage
of its growth any thing but a Vertebrate, or an Articulate any thing but
an Articulate, or a Mollusk any thing but a Mollusk, or a Radiate any
thing but a Radiate.” Geologically, also, we see no transition between
types. “In the earliest fossiliferous strata there were the three
classes of Radiates, two of the classes of Articulates, and one of the
classes of Vertebrates.” The Geographical Distribution of animals proves
the same thing. Thus Agassiz proves that the Series of Rank, of Growth,
of Time, and of Geographical Distribution all show that there is no such
gradation as transmutation implies, and that the connection between
different kinds of living things is not a material connection, but only
an intellectual one, indicating the plan of the Great Architect.[8]
5. In all forms of life which have yet come under human observation, the
origin has not been by transmutation, but by parental derivation.
Animals and vegetables all come from parents of similar organization. If
ever transmutation was the law of origin, it has been changed, and the
law of parentage is now supreme. But a change of law is inconsistent
with the theory of evolution. Unless the law had been changed, species
would still originate by transmutation, if ever they had such origin.
Such transmutation has never been observed. The Egyptian monuments prove
that the animals of earliest history remain unchanged, and Agassiz has
shown from the coral reefs in Florida that the animals of the Gulf of
Mexico remain the same as when these deposits began. Even the varieties
which man secures by “artificial selection” revert to the original type
when the modifying circumstances are removed. Transmutation has not a
single fact to prove it. At best it is but a theory, and one which all
the facts known render most improbable.
6. The geological evidence shows the entire absence of intermediate
varieties between species, which intermediate forms Mr. Darwin himself
admits to be necessary to establish his theory of natural selection. He
claims that the geologic record is defective, and that when it is better
known it will exhibit these forms. But among more than 30,000 species,
many of them represented by thousands of individuals, some of the
intermediate forms would occur, if any ever existed. Professor Pfaff has
shown the improbability of the terminal links only of the chain being
preserved by applying the calculus of probabilities. If 100 individuals
of each species have been found, and 10 intermediate varieties existed,
(a smaller number than Darwin claims,) the probability against the
exclusive appearance of distinct species is as 1:10¹⁰⁰, (1:1 with 100
ciphers annexed.[9]) Professor Marsh claims to have discovered
apparently intermediate forms between the Palæotherium and the horse,
but the proof that the Palæotherium, or the bones referred to, belonged
to the progenitors of the horse has not been shown, any more than the
juxtaposition of bones of the horse, the zebra, and the ass, would prove
them to be derived from each other. If it were proven, although it would
show great variability in that species, it would not establish
transmutation.
7. Geology shows that some of the first forms of life are also the
latest, as the corals. If transmutation be true, in the struggle for
existence they should have disappeared by being changed into something
higher. That they have not makes against Evolution.
8. Believers in transmutation claim that all living came into existence
by the gradual modification of a primitive germ, and they find
plausibility for this in the development of a single bioplast into the
various tissues of an animal. Another analogy is found in the
development of the embryo. As the tadpole is first a fish, and then a
tailed amphibian with lungs and gills, before it becomes a frog, so they
deem that the history of the embryo recapitulates the transformations of
the species. This sort of theorizing has given rise to numerous efforts
to arrange the family tree of each species—a branch of biological
speculation termed _Phylogeny_—and examples of it may be found in
Darwin, Haeckel, etc. Mr. Huxley, although a believer in Evolution,
declares that such summaries of descent are little better than
guess-work.[10]
9. Many instances of complicate and perfect structure occur both in the
vegetable and animal kingdoms which have no similar structure preceding
nor following them. No scheme of evolution, nor survival of the fittest,
can account for them. The mechanism of the leaf of Venus’s fly-trap, and
of Nepenthes, the nettling threads of Hydroid polyps, and the peculiar
disk-like hairs on the thigh of the male water-beetle, (_Dytiscus
marginalis_,) are a few out of almost numberless instances of this fact.
The most perfect dental apparatus in the animal kingdom, the teeth of
Echinus, called Aristotle’s lantern, is also the first to appear, if we
trace animal life from its simplest forms, and there is nothing like it
elsewhere. Like Melchizedek among priests, it has no predecessor and no
successor. Its form and arrangement are a protest against the theories
of material development. In the Rotifer, again, the typical form and
structure of the teeth are entirely different, being an anvil and two
hammers. In the Gasteropods they are spiny tongues.
10. Evolutionists find it difficult, if not impossible, to account for
the first origin of living matter. The boldest and most logical among
them maintain that it began spontaneously out of non-living matter.
Some, like Sir W. Thompson, suppose that the germs of living things were
transported to our globe from some other. Others, as Darwin, hold to the
creation of a single germ, or a few germs, from which all have
developed. The doctrine of the spiritual origin of living things is
beset with no such difficulties as the mechanical theory. While it
admits a unity of plan resulting from the superintending intelligence of
an all-wise Creator, it sees in living things a true diversity also. It
is hard to imagine how a naturalist can think of “differentiation”
without acknowledging a cause of variety _ab extra_, (from without.)
11. The evidence adduced in favor of spontaneous generation is always of
one kind. A quantity of animal or vegetable infusion is boiled in a
flask, which is then hermetically sealed. After a time minute forms of
life are found on a microscopic examination of the fluid. It is taken
for granted that all living germs are destroyed by boiling water, and
that therefore the organisms seen after a few days are developed
spontaneously. But Messrs. Döllinger and Drysdale have shown that some
germs remain alive after exposure to a temperature of 300° F., and
Pasteur has found that stopping the necks of the flasks with cotton
wool, so as to filter the air from all germs, prevents the appearance of
Infusoria, as well as of decay, in fluids well adapted to such
organisms. Professor Tyndall has also experimented with a great variety
of fluids in air so deprived of floating germs as to be optically pure,
and has had similar results. So that we may consider the question to be
scientifically settled, and that all living beings come from similar
parentage, or, as Virchow expresses it, “_omnis cellula e cellula_,”
(every cell is from a cell.)
12. Parentage is of two kinds, sexual and non-sexual. In the first, we
sometimes find the sexes distinct, as in the higher animals, and
sometimes united in the same individual, as in the stamens and pistils
of most flowers, and as in some animal forms.
Non-sexual generation is seen mostly in the simpler forms of animal and
vegetable life, and as it throws light on many of the phenomena of
nature which would otherwise be obscure, we notice this form of
reproduction here in a general way, reserving special instances until we
treat of the life-history of each class.
13. In referring to the Vorticella, or bell-shaped animalcule, in our
first chapter, mention was made of its increase by self-division. The
mass of bioplasm of which it is composed separates into two masses,
which become separate individuals. This mode of increase is called
_Fission_, and is quite common among the minuter forms of life. In
_Sarcina ventriculi_, a sort of vegetable parasite, the division is into
fours, or four times four.
14. A variety of fission, called _Gemmation_, or _Budding_, is often met
with. A portion projects from the mass, and separates to begin an
individual existence. Thus in the fresh-water polyp, or Hydra, a bud
gives rise to an organism like the parent, which becomes detached and
independent. Sometimes the product of buds remains attached, as in
plants, and in the Foraminifera. In other cases the budding is internal,
and the progeny may or may not remain attached to the parent.
15. _Alternation of generations_ is a term given to express a mode of
reproduction in which “the parent finds no resemblance in his progeny
until he comes down to his great-grandson.” The Jelly-fish, or Medusæ,
from the huge masses cast up by the waves of the sea-shore, to the tiny
bell no bigger than a pea, are developed in this manner. A ciliated
germ, like some of the Infusoria in form, swims about awhile, then
becomes attached, elongates, and develops into a polyp like the Hydra.
The polyp becomes wrinkled and subdivides until it looks like a pile of
saucers with scalloped edges. This breaks into segments, each of which
becomes a jelly-fish, which enlarges and produces fresh germs. Fig. 5.
This form of reproduction differs from metamorphosis, such as a
butterfly undergoes in passing from the egg to the perfect insect, or as
most animals pass through in the embryonic state. The caterpillar
becomes a butterfly, but the hydra-like individual referred to produces
a number of Medusæ.
[Illustration: FIG. 5.—
Diagram illustrative of the Development of Hydrozoa.
(The specimen is one of the Lucernaridæ.)
1. Ciliated embryo or “planula.”
2. Hydra tuba, showing single individual.
3. Hydra tuba undergoing segmentation.
4. The segmentation becoming more complete.
5. More advanced stage, in which the tentacles are developed
from the first or basal segment.
6. Segmentation complete, giving rise to a free swimming Medusoid.]
16. _Partheno-genesis_, or virgin production, denotes the production of
new individuals by virgin females without the intervention of a male.
The Aphides, or plant lice, so often found parasitic on plants at the
close of autumn, consist of winged males and wingless females. The ova,
or eggs, are dormant through the winter, and the young hatched in the
spring are sexless, but produce viviparously a brood like themselves,
and this generation produces another, and so on for ten or twelve
generations, the last brood being male and female as at first. Many
other tribes of insects afford examples of partheno-genesis.
17. The subject of this chapter brings us to some of the deepest
mysteries of creation. The parentage of all living, and the various
modes in which the principle of parentage is manifested—such topics are
wonderful seed-thoughts. It is not likely that we shall ever understand
fully the repetition of individuality, but we see enough to indicate
some of the plans of the Designer of all. “Lo! these are parts of his
ways . . . but the thunder of his power who can understand?”
Some analogies between the teachings of biology as to the genesis of
living things, and some of the statements of Scripture, may be readily
traced. Mr. Joseph Cook has been sharply criticised for comparing the
birth of Jesus, as revealed in the Gospels, with partheno-genesis; yet
he had reason for so doing, nor is he alone in his opinion. In President
Dawson’s “Origin of the World” we read, “It is curious that the Bible
suggests three methods in which new organisms may be, and, according to
it, have been, introduced by the Creator. The first is that of immediate
and direct creation, as when God created the great _Tanninim_, (whales.)
The second is that of mediate creation, through the materials previously
existing, as when he said, ‘Let the land bring forth plants,’ or ‘Let
the waters bring forth animals.’ The third is that of production from a
previous organism by power other than that of ordinary reproduction, as
in the origination of Eve from Adam, and the miraculous conception of
Jesus.”—P. 229.
“The Bible indicates some ways in which living creatures may be
modified, or changed into new species, or may give rise to new forms of
life. The human body is, we are told, capable of transformation into a
new or spiritual body, different in many important respects, and the
future general prevalence of this change is an article of religious
faith. The Bible represents the woman as produced from the man by a
species of fission, not known to us as a natural possibility, except in
some of the lower forms of life. The birth of the Saviour is represented
as having been by partheno-genesis, and if it had pleased God that Jesus
was to remain on earth as the progenitor of a new and higher type of man
to replace that now existing, this might be regarded as the introduction
of a new species.”—P. 378.
It certainly disarms skepticism and strengthens the probability of Bible
history, to find such analogies between the natural world and the record
of revelation.
Living beings are not fortuitous nor necessary groupings of atoms,
either mechanical, as Monism teaches, or monads of force, as Leibnitz
wrote, but sparks of spiritual existence, given off voluntarily from the
Eternal Parent, having various powers and capacities, yet each capable
of pressing the fleeting atoms of matter into its service during the
period alloted to it in the world. Of all living beings man is nearest
like the Great Father, in whose image we were created, and who, when
heart and flesh—body and animal life—shall fail, may be the strength
of our hearts and our portion forever.
“For we also are his offspring.”
CHAPTER IV.
T I S S U E F O R M A T I O N .
In regard to the physical universe, it might be better to
substitute for the phrase “government by laws,” “government
_according to_ laws,” meaning thereby the direct exertion of the
Divine Will, or operation of the First Cause in the Forces of
Nature, according to certain uniformities which are simply
unchangeable, because, having been originally the expression of
Infinite Wisdom, any change would be for the worse.—DR. W. B.
CARPENTER.
1. A TISSUE is a structure which presents a special form and serves a
special purpose. Thus we find in plants cellular and woody tissues, and
in animals muscular, nervous, connective, and epithelial tissues, etc.
From tissues are formed organs, as the circulatory, respiratory, or
digestive organs. A collection of organs serving a common purpose is
called a system, as the nutritive, generative, or nervous systems. The
union of systems in a co-ordinate organism, or the equivalent of such a
union, forms an individual. An individual among the higher forms of life
is a very complex arrangement of systems and organs; but in the lower
forms more simple arrangements prevail, which may be considered
equivalent, or representative, of complicated organs, as in the
Rhizopods, referred to in Chap. II., Sec. 5.
2. In the formation of tissues, the peculiar living properties of
bioplasm already described; the physical agencies of light, heat,
electricity, and moisture; chemical reactions such as are common to
inanimate substances; and certain properties called _osmose_ and
_molecular coalescence_, all combine, so as to render the study of some
tissues quite complex. In other cases the mode of formation is readily
traced.
3. The action of physical stimuli, as heat, etc., upon bioplasm itself
is yet very imperfectly known. Light is not essential to its
development, as is seen in the growth of fungi, the cells of the
interior of organisms, and of the embryo in the dark. Many experiments
on bioplasm have shown that a moderate increase of temperature quickens
its movements, and a corresponding depression retards them. Electrical,
mechanical, and chemical stimulation have similar effects to heat. Yet
the action of these stimuli vary in different cases. The motions of
amoebæ are arrested by iced water, and recommence on raising the
temperature, yet the segmentation of trouts’ eggs proceeds well in iced
water, but in a warm room they soon die.[11] If the change of intensity
in the stimulation be made gradually, and not suddenly, the living
matter will sometimes adapt itself to it without serious disturbance.
Animals have been frozen and revived, and there are instances on record
of men enduring for a considerable time without much inconvenience the
heat of ovens raised to 500° F.
The influence of light, heat, and electricity upon formed material of
different kinds is very great, but the complexity of the organism and of
the phenomena render it difficult to know what part is supplied by the
bioplasm and what by its product. The vegetable bioplasm of the interior
grows and reproduces its kind, but the green chlorophyll which it forms
beneath the epidermis, especially in the leaves, under the influence of
light alone breaks up carbonic acid for the supply of carbonaceous food.
The influence of the more luminous rays, as the yellow and orange, is
greater in this respect than the others. Gardeners blanch certain plants
by raising them in the dark, yet in the first part of the germination of
seeds Light is injurious rather than beneficial. The influence of Light
upon the direction of the growing parts of plants, the opening and
closing of flowers, etc., may be chiefly owing to its influence upon the
chlorophyll referred to above, or it may be in some degree a direct
mechanical stimulus. The same amount of Light, however, is not required
for all plants. Some require a very different amount than others. Among
animals Light has considerable influence upon colors, and still more
upon the process of development. Persons who live in cellars or in dark
streets are apt to produce deformed children, while recoveries from
disease are promoted by the access of light.
To every species of plant and animal there is a congenial and favorable
temperature, although great varieties exist in this respect, as well as
in the power of adaptation to extreme conditions. Many plants, for
example, perish with the slightest frost, yet the little fungus (Torula)
which is the principal agent in yeast, does not lose its vitality at 76°
below zero, although requiring a somewhat elevated temperature for its
active growth.
Electricity possesses the power of exciting the contractility of the
muscular fibers and the nervous force in animals in a remarkable degree.
It has, however, mechanical, chemical, and thermal influence, in
addition to its own special power, so as to be a very valuable agent in
scientific medicine; yet the nature of its relation to the living
organism is not yet understood.
[Illustration: FIG. 6.—Bladder containing syrup, attached to a tube and
plunged in a vessel of water. The inward motion of the water (endosmose)
exceeds the outward movement of the syrup, (exosmose,) and presses the
fluid up the tube. ]
In every organized being there is an incessant play of most varied
actions. Buffon well said, “The animal combines all the forces of
nature; his individuality is a center to which every thing is referred,
a point reflecting the whole universe, a world in miniature.” It is a
one-sided philosophy, however, which sees in the living thing nothing
more than the forces which are outside of it and play upon it, and are,
to a great degree, subject to it.
4. _Osmose_, or osmotic action, is a property of animal and vegetable
membrane, and of some other porous or soft materials, by which liquid
substances may be separated from each other. If two liquids (or gases)
capable of mixing with each other are separated by paper, caoutchouc, or
a bladder, one liquid being suspended in a bladder, or in a cylinder
with its lower end tied over with bladder, etc., and immersed in the
other liquid, the liquid within will pass through the bladder into the
other, (_exosmose_,) or the liquid without will pass into the bladder,
(_endosmose_,) or both endosmose and exosmose will take place at the
same time until there is an equal proportion of liquids on either side.
(Fig. 6.) These phenomena are owing to the physical attraction the two
liquids have for each other and for the membrane separating them.
Crystallizable bodies, as salt, niter, etc., when in solution, and
substances allied to them, as hydrochloric acid, and alcohol, pass
readily through membrane; but bodies which do not crystallize, but
assume the gelatinous form, as gum, starch, albumen, hydrate of alumina,
etc., pass through, if at all, with great slowness. Such bodies are
called _colloid_, or glue-like. Osmose occurs through all jelly-like
bodies, as bioplasm, as well as through fully formed membrane, and in
this manner various liquids are absorbed or imbibed by the tissues.
5. _Molecular coalescence_ is a term applied to the modification of
ordinary forms of inorganic particles which occurs when they combine in
the presence of organic matter. Thus it has been found that the
crystallization of certain salts of lime, as the carbonate, when
occurring in a solution of some organic colloid, as gum-arabic, albumen
of eggs, blood-serum, and gelatine, is so modified by such a solution as
to resemble many of the calcareous deposits found in nature.
The bottom of the middle and northern parts of the Atlantic Ocean is
found by the deep-sea dredge, even at the depth of nearly three miles,
to be covered with a sort of slimy ooze, which Prof. Huxley formerly
deemed to be of animal nature, and termed _Bathybius_. More recent
investigations have led him to change this opinion. It is regarded as a
gelatinous inorganic secretion, or a product of Diatoms, a family of
minute Algæ. In this slime great numbers of globular, shell-like
microscopic masses are found, similar to those in the chalk strata of
the earth’s crust. By experiments in molecular coalescence similar forms
have been produced artificially.
Spicules, like those in the skin of certain marine animals, have also
been formed by molecular coalescence, as well as laminated plates like
cuttle-fish bone. It is quite probable that many calcareous deposits in
tissues, as in the shell of the bird’s egg, in the scales of fishes, as
well as in bone and teeth, may be thus accounted for. The presence and
contact of living colloid matter modifies the ordinary laws of
crystallization, and produces forms differing according to the endowment
of the bioplasm.
6. In vegetables most of the organs are composed of _cellular tissue_,
or a congeries of cells. The surface of the cell, which originates by
fission from bioplasm, is changed into _membrane_, or cell-wall, while a
_nucleus_, (one or more,) now generally regarded as a concentration of
vital power, appears inside. Within the nucleus, another spot, the
_nucleolus_, is sometimes seen. (Fig. 7.) The cell itself presents the
appearance of a bladder full of fluid or semi-fluid material, in the
midst of which the nucleus is visible.
[Illustration: FIG. 7.—Vegetable cell, with nucleus and nucleolus.]
7. Many simple vegetable forms consist of a single cell, the membranous
wall of which is a species of formed material called _cellulose_, a
substance analogous to starch. Within this membrane the bioplasm is, as
it were, imprisoned, yet receiving pabulum by endosmose, or through
pores left in the membrane, its vital functions remain. In the higher
plants, as the palm or the oak, the structure is but an aggregation of
cells, some of which have been modified in form to serve special uses.
8. Near the vegetable cell-wall the bioplasm appears less fluid than in
the middle of the cell, and certain chemical agents cause a partial
separation from the membrane, so as to present, under the microscope,
the appearance of a secondary and gelatinous membrane—the _primordial
utricle_.
In some vegetable cells the molecular movement of the contained bioplasm
is quite evident, and has received the name of _Cyclosis_. It may be
seen under the microscope in the stinging hair of the nettle, and in
hairs from the calyx of _Tradescantia Virginica_, etc. (Fig. 8.)
[Illustration: FIG. 8.—Three cells from the hair of a potato, showing
Cyclosis. Bioplasmic threads proceed from the nuclei, along which the
current flows, in the direction of the arrows.]
9. Within the cell-wall the bioplasm may be transformed into
chlorophyll, or green coloring matter, into starch, gum, oil, resin,
sugar, or other kind of formed material or mineral substances may
crystallize in the cells, forming what are known as raphides. The
variety of vegetable products of this kind is very great. (Figs. 9 and
10.)
[Illustration: FIG. 9.—Cellular tissue of Cereus variabilis,
containing: _a._ _a._ Jelly. _b._ Crystals. _c._ Starch-granules. ]
[Illustration: FIG. 10.—_a._ _b._ Cells of a potato, containing starch.
_c._ Starch-grains apart. _d._ _e._ _f._ Wheat-starch in different
positions. ]
10. There is often a deposit of silica on the cell-wall, as in grasses,
horsetails, and diatoms. Some of these latter are beautifully marked
with lines and dots, rivaling the most complicate patterns of
engine-turned engraving.
[Illustration: FIG. 11.—Woody fiber. ]
[Illustration: FIG. 12.—Glandular fiber _a._ External appearance. _b._
The sides of two tubes, or fibers, in contact. _c._ _d._ Lenticular
cavity between the tubes. ]
11. Cell-membrane, as all other kinds of formed material, grows by
addition inside, so that the inner layer is the youngest. The formed
material may get so thick that nutrition ceases and the bioplasm is
wholly transformed, or dies. The solid deposit which fills up the cells
of woody fiber is known as _sclerogen_, or woody tissue. (Fig. 11.) In
Coniferous plants the fibers are marked with depressions, or concave
spaces, (glands?) the centers of which are penetrated, as if some sort
of special communication existed between the bioplasm of contiguous
cells. (Fig. 12.) Sometimes sclerogen is deposited within the cell-wall
in such a manner as to produce dots, or pores, or rings, or spiral
fibers, which give names to the several kinds of Cells. (Fig. 13.)
[Illustration: FIG. 13.—Annular and dotted cells. ]
[Illustration: FIG. 14.—Various forms of cells: _a._ Conical. _b._
Oval. _c._ Prismatic. _d._ Cylindric. _e._ Sinuous. _f._ Branched. _g._
Entangled. _h._ Stellate. _i._ Fibro-cellular tissue. ]
[Illustration: FIG. 15.—Annular, dotted, and spiral vessels and ducts.
]
[Illustration: FIG. 16.—_a._ Transverse stem of Endogen, (Palm.) _b._
Of Exogen, (Buckthorn.) _c._ Transverse and longitudinal section of
Maple in the beginning of the second year. ]
12. Vegetable cells are of various shapes, according to the purposes
they subserve. They may be conical, oval, prismatic, cylindrical,
sinuous, branched, entangled, or stellate. (Fig. 14.) Tubes, or vessels,
are formed of elongated cells. Sometimes such cells join end to end, and
the partition being removed by absorption, a long tube is formed. Such
vessels may be dotted, reticulated, annular, or spiral, from the deposit
of woody tissue, or sclerogen. (Fig. 15.) In the stem of Endogenous
plants, as palms, etc., bundles of fibro-vascular tissue occur among a
mass of cellular tissue; but in Exogens, as the maple, oak, etc., we
find a more regular arrangement of pith, medullary sheath, wood, bark,
and medullary rays. (Fig. 16.) The pith is the cellular tissue of the
center; the medullary sheath a ring of spiral vessels round the pith,
which sends projections through it to form the medullary rays; the wood
consists of concentric layers of woody and vascular tissue; and the bark
is made of cellular materials, sometimes containing branching vessels
(laticiferous tissue) conveying milky juice.
[Illustration: FIG. 17.—Perpendicular section of Melon-leaf: _h._
hairs; _s t._ stomata; _f v._ fibro-vascular tissue of the veins. ]
[Illustration: FIG. 18.—Epidermis of Madder, with stomata. ]
13. Leaf-tissue is made up of cells, with cavities, fibro-vascular
bundles, and epidermis. (Fig. 17.) The latter is a sort of skin composed
of compressed cells, among which are found openings, or pores,
(_stomata_,) each guarded by two or more elastic cells which regulate
evaporation and respiration by their expansion. (Fig. 18.)
From the surface of the epidermis arise hairs, formed of minute
expansions of cellular tissue. They are of various forms. Some of them
secrete volatile oil, others, as the nettle, an acrid fluid. They often
form microscopic objects of great beauty. (Fig. 19.)
[Illustration: FIG. 19.—Various forms of vegetable hairs. ]
The poet Goethe first clearly showed that the various parts of the
plant, from the seed to the blossom, are but modifications of the leaf.
All the parts of a flower, calyx, corolla, stamens, and pistil, are only
leaves adapted for peculiar functions. They were not originally leaves,
and afterward transformed, but they are formed of the same elements, and
arranged upon the same _plan_, and in the changes which they undergo and
the relation they bear to each other, they follow the same laws as
leaves do.
All leaves are arranged upon the stem after two leading patterns—the
_whorl_ and the _spiral_; but as by teasing out the whorl we get the
spiral, and by compressing the spiral we get the whorl, we may regard
them as essentially the same.
14. In the animal kingdom, with the exception of those simple forms of
life already described, which increase by fission or budding, (Chap.
III., Sec. 12, 13,) the germ of all the tissues is first a piece of
simple bioplasm derived from the vesicles of the ovary. This is
fertilized by fusion with similar bioplasm derived from the male. It
then acquires a membrane, and exhibits a nucleus and nucleolus, as in
the case of the primitive vegetable cell. Changes, however, take place
in the animal ovum which we do not observe in the vegetable, and these
changes differ also in the different classes of animals. In the higher
classes the ovum separates into two spheres, which sub-divide into four,
then into a mulberry-like mass of cells, or _morula_. (Fig. 20.) These
cells in the vertebrates arrange themselves into a layer lining the
vitelline membrane, on one side of which is a sort of pouch, or
_blastoderm_, consisting of three layers of cells, the epiblast, the
mesoblast, and the hypoblast. The first of these produces the skin, the
middle one the nervous, muscular, and vascular systems, and the latter
the lining of the intestinal and respiratory organs.
[Illustration: FIG. 20.—Segmentation of Mammalian Egg. A. Division into
halves. B. Further subdivision. C. Mulberry mass, or Morula. ]
The alimentary canal is at first a straight tube closed at both ends. As
it grows faster than the body it is thrown into a spiral coil, and at
several points it dilates, to form the stomach, etc. The mouth is
developed from an infolding of skin. The liver is an outgrowth from the
digestive tube, at first a cluster of cells, then of follicles, and
finally a true gland. The lungs first appear as minute buds from the
upper part of the alimentary canal, or pharynx.
15. The transformation of the cells of the blastoderm into various
animal tissues is effected in various ways.
_a._ An interstitial deposit of formed material may occur in the
bioplasm, or cell. Thus oil-globules, pigment, or vacuities may greatly
modify the appearance and actions of the cell. The action of tannin, or
boracic acid, etc., upon the red blood disks of animals, shows each of
them to be really double, having a continuous interstitial substance
deposited in each disk. Prof. Brucke, who first investigated this
structure, called the parts of the disk respectively, the _zooid_ and
the _œcoid_, the former being the part which, in the living state,
contains also the hæmoglobulin, or red coloring matter.
_b._ Cells are sometimes found scattered through an intercellular
material, the product of cells or of cells transformed and fused
together. This intercellular mass may either remain continuous, or split
up into fibers. In this way fibrous connective tissue, cartilage, etc.,
may be formed. (Fig. 21.)
[Illustration: FIG. 21.—Connective-tissue. A. White and yellow fibers.
B. Developing Cells of connective tissue. ]
_c._ The cells which cover surfaces, and through which all interchange
between the body and the external world is carried on, are called
_epithelial_. They differ in shape, either from mutual pressure or
function, some being flat and squamous, (or scaly,) and others columnar.
Some of the latter have cilia, or hair-like projections, whose motions
produce a current over the surface. Thus the skin, or mucous membrane,
is not a continuous membrane, but made up of cells, the nuclei of which
exhibit the remains of the bioplasm or living matter from which they
sprang. (Fig. 22.)
[Illustration: FIG. 22.—Epithelial cells. 1. Squamous epithelium from
the skin, showing the change from bioplasm to horny scurf. 2.
Tessellated Ep. from serous membrane. 3. Columnar Ep. from intestine. 4.
Ciliated Ep. from air-passages. ]
_d._ In bone and other hard tissues, as the teeth, the intercellular
substance is solidified by salts of lime deposited in a modified form by
molecular coalescence. Sec. 3. In this case the bioplasm, or cell, is
limited to certain spaces, or _lacunæ_, and receives nourishment through
small canals, or _canaliculi_. (Fig. 23.)
[Illustration: FIG. 23.—Transverse section of a long bone. _a._
Haversian canal. _b._ Concentric laminæ. _c._ Laminæ of connection. _d._
Lacunæ, with their system of tubes.]
_e._ Some fibrous structures may be formed by moving particles of
bioplasm, leaving behind them a thread of formed material. In voluntary
muscular fiber this formed material is duplex, and in certain
nerve-ganglia the fiber is spirally coiled around another by the forward
and rotary motion of the bioplasmic cell.
16. We may consider the living organism, either animal or vegetable, as
a building, a workshop, or a laboratory, and in each view the cell, or
bioplasm, plays the most important part.
If we regard an organism as a building, the cells are the constituent
parts, or building-stones. The most simple forms of life, as we have
said, are single cells, while the more complex are composed of myriads
of these cells, with the materials produced by them, arranged in various
forms, according to the nature of the individual. Thus in the
yeast-plant (_Torula_) the cells touch each other at only one or two
points, while the wood-cells of higher plants adhere in their entire
extent by means of formed material. Vessels, or ducts, are either
elongated hollow cells, or are formed by the union of cells. In every
structure, except the most primitive, we also find secret chambers and
grottoes which we should not previously have suspected; and where
strength is needed, provision is made for it by the deposit of hard
substance, and by the interlacing of fibers, once cellular, in a most
wonderful manner. Even the temple of Solomon, in all its glory, was not
more complete in architectural details than the structure of many of our
plants and animals. As that temple was said to have been erected without
the sound of hammer or saw, so the animated edifice is built silently,
story after story, from day to day, until its life-work is accomplished.
Such a structure is a workshop, as well as a building. There is
something in it full of peculiar activity, altogether different from the
forces which belong to metals and stones, or other inorganic bodies. We
call it Life, and the more we observe its powers the more we shall be
convinced that it is the Master, and not the slave, of matter, and that
the forming power is different from the thing which is formed. It makes
its own workshop and its own tools, and compels the physical forces of
inorganic nature to assume new and different relations, so as to serve
its own purposes. It forms its own building-stones, and elevates them to
their places against gravity, removes such as are in decay and replaces
them with others, and strengthens such parts as are most exposed to wear
or strain.
The organism is also a laboratory. There Life, as a subtle Alchemist,
sits and transmutes the chemical elements around it into new and useful
forms, in a way which surpasses all our knowledge. Thus from the same
materials, and under the same conditions of light, heat, and
electricity, one cell will make starch, another fat, another sugar,
albumen, flesh, coloring-matter, acids, or alkalies; nay, even in parts
of the same cell different materials may be produced.
17. Every glance into the marvels of organic structure reveals new
wonders. As in the remote regions of space we may trace myriads of suns,
with nebulous films and world-islands, which hide from us what is behind
them, so here every step reveals something new and gives glimpses of
something beyond. The details of Histology would fill a large volume,
and even an ordinary life-time is insufficient to do more than to gather
up a few facts and arrange them in proper relations, yet the pursuit of
knowledge continually brings us nearer to the fountain of Absolute
Truth. To the microscope, even more than to the telescope, belongs the
introduction of the inquirer into the arcana of the universe. If it does
not lead us outward into realms of space, which exhibit the same
relations of scientific and abstract truth as the world on which we
dwell, it leads us inward toward the foundations of our own existence,
and shows that the relations of truth are as perfect in the descending
as in the ascending sphere. If we see not life itself, we see its first
beginnings, and the process of its development. If we see not Nature in
her undress, we trace the elementary warp and woof of her mystic
drapery. From both telescope and microscope alike we learn that the
widening sphere of knowledge is constantly encircled by the unknown, yet
through them we see above and beneath us a myriad instances of the skill
and providence of a Great Designer, who is God and Father of all. The
living atom shines with truth no less than the star.
“Forever singing as they shine,
The hand that made us is divine.”
CHAPTER V.
T Y P E S O F C O N S T R U C T I O N .
. . . Much less, then, have we any idea of the substance of God.
We know him only by his most wise and excellent contrivances of
things and final causes; we admire him for his perfections; but
we reverence and adore him on account of his dominion: for we
adore him as his servants; and a god without dominion,
providence, and final causes, is nothing else but Fate and
Nature. Blind metaphysical necessity, which is certainly the
same always and every-where, could produce no variety of things.
All that diversity of natural things which we find suited to
different times and places could arise from nothing but the
ideas and will of a Being necessarily existing.—SIR ISAAC
NEWTON’S _Principia_.
1. Our imperfect knowledge of nature must always give a provisional
character to our classifications. If they present the knowledge we
possess in a useful and compact form, it is all they can be expected to
do. Further knowledge may confirm or overthrow the most perfectly
symmetrical system. Tennyson has well sung:
“Our little systems have their day,
They have their day and cease to be,
They are but broken lights of thee,
And thou, O Lord, art more than they.”
—_In Memoriam._
Yet an arrangement may be true although imperfect. We may see plainly
the leading outline, while a myriad details may be unknown.
2. In attempting to arrange organic forms it is impossible to place them
in a single line, like the steps of a ladder, according to structural
rank. There are no such gradations in nature as some imaginations have
conceived. There are so many relationships, both of structure and of
function, that a single series is out of the question. There are many
series, and series, also, within series. Organic forms seem to be placed
in radiating groups rather than lines, each group being connected, not
with two groups merely, one above and the other below, but with several.
Living things are, therefore, best studied in groups, or circles,
according to prominent types or representative forms. These groups will,
doubtless, be unequal and dissimilar, and will be far from representing
the grade of organization; yet they will be of great use, not only to
the memory, but also in indicating the general order of the universe.
3. The unity of organic nature is seen in the similarity of bioplasm, or
living matter; its variety is shown in the multiform arrangements of
structure in living beings. That all this variety can be intelligently
connected together in a few comprehensive groups, exhibiting plans of
structure, is proof positive of the intelligence of the creative power.
Agassiz has well said, “If these classifications are not mere
inventions, if they are not an attempt, to classify for our own
convenience the objects we study, then they are thoughts which, whether
we detect them or not, are expressed in Nature—then Nature is the work
of thought, the production of intelligence, carried out according to
plan, therefore premeditated—and in our study of natural objects we are
approaching the thoughts of a Creator, reading his conceptions,
interpreting a system that is his and not ours.”
4. _Types_ are comprehensive natural groups of living forms, founded on
plans of structure or structural ideas. _Classes_ comprise all forms
which agree simply in a special modification of the type to which they
belong. The type represents the plan, but there may be several ways of
executing the plan, and these ways illustrate the classes. In human
works of art “there are certain architectonic types, including edifices
of different materials, with an infinite variety of architectural
details and external ornaments; but the flat roof and the colonnade are
typical of all Grecian temples, whether built of marble or granite or
wood, whether Doric or Ionic or Corinthian, whether simple and massive
or light and ornamental; and, in like manner, the steep roof and pointed
arch are the typical characters of all Gothic cathedrals, whatever be
the material or the details. The architectural conception remains the
same in all its essential elements, however the more superficial
features vary. Such relations as these edifices bear to the
architectural idea that includes them all, do classes bear to the
primary divisions,” or types.[12] Thus Fishes, Amphibians, Reptiles,
Birds, and Mammals are classes under the Vertebrate type of animal life.
An _Order_ is a group of families, or genera, related to one another by
a common structure. Thus Cats, Dogs, Hyenas, and Bears are linked
together, since their teeth, stomachs, and claws show the carnivorous
habits of the order Carnivora.
A _Family_, or _Tribe_, does not allude to the progeny of a known stock,
but refers to a group of genera having similarity of form. The term was
first introduced into Botany in France, in connection with what is
called the natural system of classification. To prevent confusion, the
similarity of form determining families should be based on structure and
not mere resemblance.
A _Genus_ is a group of species having the same essential structure.
Thus the allied species, Cat, Tiger, and Lion, belong to one genus.
A _Species_ is the smallest group of individuals which can be defined by
several constant characteristics. They are so alike that it is possible
for them to have descended from one pair. A cross between two species,
as the Horse and Ass, is called a _hybrid_; as the Mule.
_Individuals_ are the units of organic life. A complete animate
existence is an individual, whether separate, as man, or living in a
community, as the Coral. When two or more individuals differ by a single
peculiarity, such as color, or outline, or size, one is called a
_variety_ of the other, as the races of Men and breeds of Cattle. A
cross between distinct races is called _mongrel_.
Vegetables and animals are separated from each other under the term
_kingdom_, and the types of structure in each kingdom are called
_sub-kingdoms_. Thus in the animal kingdom we have the sub-kingdoms of
Vertebrates, Radiates, etc.
There are no such _things_ as genus, species, order, class, etc. They
are but abstract terms, expressing relation to a plan, or the harmony of
intelligent design which presides over all things.
5. A real type, or plan, includes all those individuals, species, etc.,
which are similar in character. But it is not always easy to determine
similarity of character. From the earliest times of history down to
Cuvier, naturalists were in the habit of regarding similarity of
external form and evident purpose as indicating analogies, and so far as
functional design is concerned, the principle may be considered right.
But purpose and plan for a purpose are different, and modern science
seeks for its types in the characters of internal structure and
development.
6. Parts, or organs, having similar origin and development, and
therefore the same essential structure, are called _homologous_; while
those which are anatomically different, though corresponding in use, are
called _analogous_. Thus in the vegetable kingdom the tendril of the
Vine, which is a transformation of the flower-stalk; that of the Pea,
which is a prolongation of the leaf-stalk; that of _Gloriosa_, which is
the point of the leaf itself; and that of _Strophanthus_, which is the
point of the petal; are all analogous, but not homologous. The arms of
Man, the fore-legs of a Horse, the paddles of a Whale, the wings of a
Bird, the front flippers of a Turtle, and the pectoral fins of a Fish,
are homologous but not analogous. The wings of the Bird, Flying
Squirrel, and Bat are not homologous, since that of the first is
developed from the fore-limb only, that of the Squirrel is an extension
of the skin between the fore and hind limbs, and that of the Bat is a
membrane between the fingers and down the side to the tail. The
air-bladder of a Fish is homologous with a lung, but analogous to the
air-chamber of the Nautilus. In the functional analogies, perhaps more
evidently than in the structural homologies, we trace evidence of
purpose, or design. “Blind metaphysical necessity,” as Newton called
Fate and Nature without God, could certainly produce no such “variety of
things” as we see here, while the unity pervading the functional
character of the different organs is plain enough proof of their being
the work of the same Artisan.
Various functions are attained by a modification of similar structure.
Thus the simplest plant differs from the most complex principally in
this—that the whole external surface of the former participates equally
in all the operations which connect it with the external world, as those
of Absorption, Exhalation, and Respiration, while in the latter these
functions are confined to certain parts of the surface. So in the
highest animals, the organs adapted to the functions of Absorption,
Exhalation, Respiration, Secretion, and Reproduction, are all composed
essentially of a membrane which is a prolongation of the general
surface, while this general surface is the sole instrument for the
performance of these functions in the lowest animals, and shows no
special adaptation for one or another of them. So that it may be
expressed as a general truth of Biology, that “throughout all animate
Creation, the functional character of the organs which all possess in
common, remains the same; while the mode in which that character is
manifested varies with the general plan upon which the being is
constructed.”[13]
In all living things the attainment of function is the cause of
modification of structure. This gives evidence of Creative plan, or
design, in direct opposition to the theory of gradual evolution of
structure, and is proof also of the essential differences between living
beings, since the plan of structure varies for attaining similar
purpose.
7. Cuvier proposed four primary divisions of the animal kingdom,
because, he said, they are constructed on four different plans. These
plans may be briefly stated as follows: “In the _Vertebrates_ there is a
vertebral column terminating in a prominent head; this column has an
arch above and an arch below, forming a double internal cavity. The
parts are symmetrically arranged on either side of the longitudinal axis
of the body. In the _Mollusks_, also, the parts are arranged according
to a bilateral symmetry on either side of the body, but the body has but
one cavity, and is a soft, concentrated mass, without a distinct
individualization of parts. In the _Articulates_ there is but one
cavity, and the parts are here again arranged on either side of the
longitudinal axis, but in these animals the whole body is divided from
end to end in transverse rings or joints movable upon each other. In the
_Radiates_ we lose sight of the bilateral symmetry so prevalent in the
other three, except as a very subordinate element of structure; the plan
of this lowest type is an organic sphere, in which all parts bear
definite relations to a vertical axis.”[14] Leuckart proposed to
subdivide the Radiates into two groups; the Cœlenterata, including
Polyps and Acalephs, or Jelly-fishes—and Echinoderms, including
Star-fishes, Sea-Urchins, and Holothurians, but Agassiz shows that the
differences between them are not differences in the plan, but merely a
difference in the execution of the plan, since both are equally radiate
in structure.
By this radial symmetry we are conducted toward the Vegetable Kingdom.
Thus in the higher _Fungi_ the disposition of organs is as radiate as in
Radiated animals. In _Mosses_ and _Ferns_ there is a spiral arrangement
of leaves around the axis, which may be considered the regular law of
growth in the higher plants, although sometimes obscured by special
modifications.
8. It is a popular error, fostered by the assertions of certain Monistic
writers, that the higher animals pass through all the phases of lower
life. This false notion is based upon too strict an interpretation of
Von Baer’s generalization in Embryology, that “a heterogeneous or
special structure arises by gradual change out of one more homogeneous
or general.” Every division of the Animal Kingdom has its characteristic
method of developing. “The Vertebrate arises from the egg differently
from the Articulate; the Articulate differently from the Mollusk; the
Mollusk differently from the Radiate.”[15] “Every grand group early
shows that it has a peculiar type of construction. Every egg is from the
first impressed with the power of developing in one direction only, and
never does it lose its fundamental characters. The germ of the Bee is
divided into segments, showing that it belongs to the Articulates; the
germ of the Lion has the primitive stripe—the mark of the coming
Vertebrate. The blastodermic layer of the Vertebrate egg rolls up into
two tubes—one to hold the viscera, the other to contain the nervous
cord; while that of the Invertebrate egg forms only one such tubular
division. The features which determine the subkingdom to which an animal
belongs are first developed, then the characters revealing its
class.”[16] Dr. Carpenter says: “The human embryo is never comparable
with a Fish, a Reptile, or a Bird, much less with an Insect or a
Mollusk. However close may be the resemblance between the embryo of Man
and the embryo Fish, there is no real correspondence between the embryo
of Man and the completed Fish. Each germ has a certain capacity of
development peculiar to itself, since _like produces like_.”
9. To attain a true knowledge of the order of creation, or of the types
of structure among organic forms, it is necessary not only to consider
internal construction and relationships, and the process of embryonic
development, but also to trace the life-history of each, and especially
the metamorphoses to which they may be subject at various periods. Among
the lower Fungi there is a kind of _polymorphism_ (_polys_, many;
_morpha_, form) frequent, by which several forms may be developed by
spores, or seeds, which have identically the same origin. Few animals
come forth from the egg in perfect condition. The embryonic Star-fish
has a long body, with six arms on a side, from one end of which the
young Star-fish is budded off. Soon the twelve-armed body dies, and the
young animal is of age. Most Insects undergo complete change of form, a
_metamorphosis_; _i.e._, exhibit four distinct stages of existence—egg,
larva, pupa, and imago. Among the vertebrates the most common and most
remarkable transformation is that of the Frog. It is first, after
hatching from the egg, a tadpole, with a tail, but no legs, gills
instead of lungs, a heart like that of a fish, a beak for eating
vegetable food, and a spiral intestine to digest it. As it matures, the
hind legs show themselves, then the front pair, the beak falls off, the
tail and gills waste, lungs are formed, the digestive apparatus is
changed to suit an animal diet, the heart is altered to the Reptilian
type by the addition of another auricle—in fact, skin, muscles, nerves,
bones, and blood-vessels vanish, being absorbed atom by atom, and a new
set is substituted.[17]
10. With the caution referred to in Sec. 1 we may present an outline of
the types of living forms.
The most general and comprehensive type is that of bioplasm, or living
matter, described in Chap. II, and characteristic of both animals and
vegetables. The next most comprehensive type of structure is that of
Vegetable forms in which the bioplasm is invested, or, as it were,
imprisoned, in each of its component cells by a sac of cellulose, or
some analogous compound, (Chap. IV, Sec. 5,) and whose most
characteristic work, or peculiarity, is its power of manufacturing
albuminoid matter out of simpler chemical elements. In Animal forms
there is no such cellulose investment, nor can they make albuminoid
matter from inorganic elements.
In the Vegetable Kingdom we may arrange organic forms under the
following general divisions, or principal types:
1.) PROTOPHYTES, or simplest vegetable forms, answering to the
_Unicellular Algæ_.
2.) THALLOGENS, which are a mere expansion of cellular tissue, without
complete distinction between stem, root, and leaves. These include
_Fungi_, _Algæ_, and _Lichens_.
3.) ACROGENS. Plants which grow in height and not in diameter.
_Liverworts_, _Mosses_, and _Ferns_.
4.) ENDOGENS. Vascular plants, in which the wood and cellular tissue are
mixed throughout, without distinct annual layers. The seed has but a
single lobe, or _cotyledon_.
5.) EXOGENS. Vascular plants having distinct annual layers of woody
fibers, and radiations of tissue from the medulla to the bark. The
embryo has two seed-lobes, or cotyledons.
In the Animal Kingdom we have the following typical forms, or
subkingdoms:
I. PROTOZOA. Simplest animal forms, being composed of bioplasmic jelly.
_Monera_, _Gregarina_, _Rhizopods_, _Infusoria_, and _Sponges_.
II. RADIATA. Radiate animals, which are subdivided into—1. CŒLENTERATA,
with distinct body-cavity, tentacles, and nettling thread-cells.
_Hydrozoa_, _Anthozoa_, _Ctenophora_. 2. ECHINODERMATA, with distinct
alimentary canal and nervous ring. _Crinoids_, _Asteroids_,
_Holothurians_, _Echinoids_.
III. MOLLUSCA. Soft unsymmetric animals. Digestive system developed.
Nervous system irregular. _Polyzoans_, _Tunicates_, _Brachiopods_,
_Lamellibranchiates_, _Gasteropods_, _Cephalopods_.
IV. ARTICULATA. Nervous ventral cord double. Limbs on same side as
nerve-cords. _Annelids_, _Crustaceans_, _Arachnoids_, _Myriapods_,
_Insects_.
V. VERTEBRATA. Double nervous system; one on upper side of alimentary
canal, the other spinal; limbs opposite nerves. _Fishes_, _Amphibians_,
_Reptiles_, _Birds_, _Mammals_, _Man_.
11. In the Frontispiece the characteristic features of biological types
are represented. In the outline section of each of the four types of
higher animals the large shaded spot shows the alimentary canal, the
dark spot the position of the heart, and the open rings the nervous
system. A diagram of the latter also accompanies each of those types.
CHAPTER VI.
P R O T O P H Y T E S .
Let no presuming impious railer tax
Creative Wisdom, as if aught was formed
In vain, or not for admirable ends.
Shall little haughty ignorance pronounce
His works unwise, of which the smallest part
Exceeds the narrow vision of her mind?
—THOMSON.
1. VEGETABLE structure has been already characterized as bioplasm
imprisoned, or invested with a cell-wall of cellulose. In some of the
simplest forms, or _Protophytes_, each cell is separate from the rest,
others form masses of cells in a sort of gelatinous or slimy investment,
while other forms exhibit a definite adhesion between the cells, so as
to prefigure a regular plant-like structure, although each cell is a
repetition of its parent-cell, and is capable of living apart.
[Illustration: FIG. 24.—Development of Palmoglœa macrococca.]
2. The life-history of simplest Protophyte is exemplified in the
_Palmoglœa macrococca_, (Fig. 24;) a sort of green scum or slime,
growing on damp stones, etc. The microscope shows this to consist of a
multitude of green cells, each surrounded by a gelatinous envelope, and
sometimes a _nucleus_, or more solid aggregation, which is considered
the center of vital activity, is seen in the cell. The green particles,
or granules, which fill the cells, are formed material called
_chlorophyll_. Throughout the vegetable kingdom the presence of
chlorophyll is necessary to enable the plant, under the stimulus of
bright sunlight, to break up carbonic acid, evolve the oxygen, and
appropriate carbon as food. In the absence of sunlight all plants become
oxidized, and evolve carbonic acid. The cells of the Palmoglœa multiply
by binary subdivision, or fission. (Chap. III, Sec. 12.) This
multiplication is an act of growth, and differs from similar
self-division in the higher plants by the purpose manifested, and the
plan for a purpose, seen in the “differentiation” of cells in the higher
orders for the production of special organs.
In these lowly plants there is a process similar to the plan of
reproduction in the more complex forms. A pair of cells will sometimes
reunite, or fuse together, first by means of a narrow bridge, and then a
larger mass, and finally a complete fusion. The mass is termed a
_Spore_, (from the Greek _spora_, a seed,) and is the primitive cell of
a new generation formed by fission.
[Illustration: FIG. 25.—Development of Protococcus:
_a._ Still form. _b._ Motile form.
_c._ Self-division and zoospores.]
3. In a form allied to the above, the _Protococcus pluvialis_, (Fig.
25,) not uncommon in rain-water, a somewhat greater variety of
conditions has been seen. It is found _still_, or quiescent, and
_motile_. In the first form the bioplasm is surrounded with a wall of
cellulose, and filled with granules of green or red chlorophyll. These
still cells multiply by self-division, each producing two, four, eight,
or sixteen new cells. The new cells are motile, having each two long
vibratile filaments or _cilia_. They may be seen swimming, tumbling, or
rotating in the water. At times they are surrounded by a sac, which may
be at some distance from the bioplasm. The motile cells may also
multiply by subdivision, and in some cases the minute primitive cells,
when set free, have very active movements, and rank as _Zoospores_,
(living spores,) or _Micro-gonidia_, (small angular particles, from
division of the bioplasm.) The varieties connected with the history of
this single plant have been sometimes described as distinct species, and
even genera of Animalcules, because of their shape and motions.
4. The family of _Palmellaceæ_, to which the forms referred to belong,
contain some kinds of singular interest. The “Red Snow,” which sometimes
colors extensive Alpine or Arctic tracts, is composed of myriads of
Protococcus cells, in a quiescent state, with the chlorophyll of a red
color. The _Palmella cruenta_, or “Gory Dew,” appears sometimes as tough
gelatinous masses of the color of coagulated blood, and extends over a
considerable area. In this way we may account for showers of flesh,
blood, etc., which are often regarded as bad omens by the ignorant.
[Illustration: FIG. 26.—Volvox globator.]
5. The family _Volvocineæ_ has been long considered of singular beauty
and interest to the microscopist. The _Volvox globator_ (Fig. 26) was
described by Leeuwenhöek about one hundred and fifty years ago, and from
its shape and rolling motion was called the globe animalcule, but its
vegetable character is now generally admitted. It is about one thirtieth
of an inch in diameter, and appears to the unassisted eye to be a little
green speck moving slowly through the water. On examining with the
microscope the Volvox is seen to be a pellucid sphere studded with
minute green spots, connected together by threads. From each of these
spots proceed two cilia, so that the entire surface of the globe is
beset with vibratile filaments, to whose combined action its rolling
motion is due. Within the globe may be generally seen from six to twenty
other globes, of varying sizes, which are set free by the bursting of
the parent globe. Sometimes a third generation may be seen within the
secondary spheres. Careful observation of the development of the Volvox
has shown that the ciliated cells referred to above, analogous to the
zoospores of Protococcus, sometimes appear like moving Amœbæ. (Chap. II,
Sec. 2.) This is not an uncommon phenomenon among Protophytes, and shows
that the bioplasm of the vegetable and animal cell have similar
properties.
[Illustration: FIG. 27.—Development of _Achyla prolifera_: A. Dilated
extremity of a filament,_b_, separated from the rest by a partition,
_a_, and containing young cells in progress of formation. B.
Conceptacle discharging itself, and setting free young cells, _a_, _b_,
_c_. C. Portion of filament, showing the course of the circulation of
granular protoplasm. ]
6. Dr. Carpenter recommends those who wish to study the development of
“zoospores,” and other phenomena of Protophytes, to have recourse to the
little plant called _Achyla prolifera_, which grows parasitically upon
the bodies of dead flies in water, etc. The naked eye perceives it as
tufts of minute colorless filaments, which the microscope shows to be
long tubes containing granular bioplasm, which exhibits the motion
called Cyclosis. (Chap. IV, Sec. 6.) After about thirty-six hours the
bioplasm accumulates in the dilated ends of the filaments, and its
endochrome, or granular coloring matter, breaks up into distinct masses,
each of which becomes a zoospore, or “motile gonidium,” with cilia, and
is set free by rupture of the wall of the parent cell. (Fig. 27.)
7. The family _Desmidiaceæ_ consists of minute Protophytes of a
grass-green color, growing in fresh water. The cells are generally
independent, but in some species remain adherent one to another so as to
form a filament. Some species have spiny projections of the outer coat,
which is of a horny consistence, as in Fig. 28.
[Illustration: FIG. 28.—Various species of _Staurastrum_: A.
_Staurastrum vestitum_; B. _Staurastrum aculeatum_; C. _Staurastrum
paradoxum_; D. E. _Staurastrum brachiatum._]
[Illustration: FIG. 29.—Economy of _Closterium lunula_: A. Frond
showing central separation at _a_, in which large globules, _b_, are not
seen. B. One extremity enlarged, showing at _a_ the double row of cilia,
at _b_ the internal current, and at _c_ the external current. C.
External jet produced by pressure on the frond. D. Frond in a state of
self-division.]
Others are notched on the sides; some, as the _Closterium_, (Fig. 29,)
are smooth. In the latter a circulation of fluid may be seen between the
cellulose coat and the “primordial utricle.” (Chap. IV, Sec. 6.) Some
consider this circulation to be caused by cilia, but it is rather
doubtful. We are inclined to regard it as an exhibition of the molecular
motion of bioplasm already described. Many of the Desmids multiply by
subdivision, but the plan is modified so as to maintain the symmetry
characteristic of the tribe. At other times multiplication takes place
by the subdivision of the endochrome into granular particles, or
“gonidia,” set free by rupture of the cell-wall.
[Illustration: FIG. 30.—_Cosmarium botrytis_:
A. Mature frond. B. Empty frond.
C. Transverse view. D. Sporangium,
with empty fronds. ]
The process of conjugation differs from that of Palmoglæa, since each
cell has a firm external envelope, which cannot coalesce with another.
In _Cosmarium_, (Fig. 30,) for example, the conjugating cells become
deeply cleft and separate, so that the contents pour out freely, at
first without a protecting membrane. At length it acquires an envelope,
and becomes a _sporangium_, or spore-case, of reddish-brown tint. It is
covered with spines, and greatly resembles certain fossil forms found in
flint called _Xanthidia_. The Closteria conjugate after a somewhat
similar manner, and it is not uncommon to find a pair in this condition,
but their sporangia are smooth instead of tuberculated or spiny.
8. The families of Algæ, called _Oscillatoriaceæ_, _Nostochaceæ_,
_Confervaceæ_, and _Conjugateæ_, may all be considered as Protophytes,
but a brief description only can be given here. The structure is
generally microscopic.
The _Oscillatoria_ are tubular filaments with partial subdivisions,
formed by the elongation of their primordial cells, occurring in fresh
and salt water, and on damp ground. They have very curious movements,
sometimes swaying like a pendulum, and at others bending at the
extremity from one side to another, or moving straight onward.
_Nostocs_ are beaded filaments lying in masses of greenish gelatinous
matter. As the jelly forms rapidly in damp weather, they have been
termed “fallen stars.” The alchemists often refer to this substance, and
it enters into many of their recipes for the pretended transmutation of
metals.
The _Confervæ_ may be found in almost every pond or ditch, but are
especially abundant in running water. They constitute the greater part
of those green threads which are found in streams, or near the
sea-shore. Each thread is a long cylinder, in which the endochrome, of a
green, brown, or purplish hue, is either distributed uniformly through
the cell, or arranged in a net-work, or spiral form. It increases by
binary subdivision in the terminal cell, as well as by zoospores
produced within the cells.
The family _Conjugateæ_ is so called because the filaments are so
constantly yoked together. They are generally found in still water. In
an early stage of growth the endochrome is diffused through their
cavities, but after a time arranges itself in regular spirals. Then
adjacent cells put forth protuberances which coalesce, and a passage is
formed between the cells. The endochrome of one cell passes over into
the cavity of the other, forming a sporangium, or spore-case. (Fig. 31.)
[Illustration: FIG. 31.—Various stages of the history of _Zygnema
quininum_: A. Three cells, _a_, _b_, _c_, of a young filament, of which
_b_ is undergoing subdivision: B. Two filaments in the first stage of
conjugation, showing the spiral disposition of their endochromes, and
the protuberances from the conjugating cells. C. Completion of the act
of conjugation, the endochromes of the cells of the filament a having
entirely passed over to those of filament _b_, in which the sporangia
are formed. ]
9. The most beautiful and interesting unicellular forms, now generally
conceded to be vegetable, are found among the _Diatomaceæ_. Their
motions caused many to regard them as animals, but naturalists now agree
in calling them Protophytes. They are called Diatoms because of their
extreme brittleness and the ease with which a chain of them may be
broken into its component cells. Like the Desmids, they are simple cells
containing endochrome, with a firm external covering. In the Diatoms,
however, this envelope is consolidated by silex, or flinty matter,
sometimes also by iron. The silicious envelope of each “frustule,” or
cell, is covered with most elaborate and beautiful marking, and consists
of two valves, or plates, closely applied to each other, like the valves
of a Mussel, along a suture, or line of contact. If the valve is
hemispherical, the cavity will be globular; if a segment of a sphere,
the cavity will be lenticular. Sometimes the central part is flattened,
and the sides turned up, so that the valve resembles the cover of a
pill-box, in which case the cavity will be cylindrical. Then, again, the
valve may be square, triangular, round, heart-shaped, boat-shaped, etc.
In many species of Diatoms the markings are so minute that they can only
be made out with the highest powers of the microscope; in others a very
moderate power suffices to exhibit the lines and dots in patterns which
rival the most elaborate works of art. (Figs. 32, 33, 34.)
In the living state Diatoms are found abundantly in every pond, rivulet,
ocean, and rock-pool. In some parts of the world they form immense
deposits.
A mud bank in Victoria Land, 400 miles long and 120 broad, is composed
of silicious valves of Diatoms. In Sweden and Norway, under the name of
_bergh-mehl_, they are used for mixing with flour for bread in seasons
of scarcity. Under the cities of Richmond and Petersburgh, Virginia, is
a deposit twenty feet thick, while the polishing slate of Bilin contains
Diatoms so small that in a single cubic inch 40,000,000,000,000 (forty
trillions) are found.
[Illustration: FIG. 32.—Arachnoidiscus Ehrenbergii. ]
The _Arachnoidiscus Ehrenbergii_, (Fig. 32,) is common on the coast of
California, attached to sea-weed. Its general appearance is that of a
glassy pill-box. The figure shows one of the ends, or frustules, covered
with delicate tracery like a spider’s web, by which the genus gets its
name, from _arachné_, a spider, and _discus_, a disk.
[Illustration: FIG. 33.—Heliopelta. ]
The _Heliopelta_, sun-shield, (from _helios_, the sun, and _pelta_, a
shield, (Fig. 33,) is a most beautiful disk, whose markings form a
regular star, the number of whose rays determine the species.
The _Diatoma vulgare_, (A., Fig. 34,) is a quite common form. The
frustules often hang together, forming zig-zag chains by rapid
self-division.
[Illustration: FIG. 34.—A. _Diatoma vulgare_: _a._ Side view of
frustule; _b._ Frustule undergoing self-division. B. _Grammatophora
serpentina._ _a._ Front and side views of single frustule. _b._ _b._
Front and end views of divided frustule. _c._ A frustule about to
undergo self-division, _d._ A frustule completely divided. C. _Isthmia
nervosa._ ]
Some species of _Grammataphora_ have delicate striæ on the borders of
each valve, which are used as tests of microscopic excellence.
The _Isthmia nervosa_ has a remarkable areolated structure, which will
repay careful examination. In its growth two cells form within the
valves, and, as they enlarge, break forth, but the silicious hoop which
joined the new frustules to the old one remains attached for a time
round one of them, causing some to appear truncated instead of round.
The genus _Navicula_ is so called from its resemblance to a boat or
little ship, (_navis_, a ship.) They are found both living and in a
fossil state. Some are striped longitudinally, and some transversely;
some are shaped like an old-fashioned letter S, as the _Pleurosigma_, in
which the striae are resolved by a highly magnifying power into
hexagonal dots.
10. In the Protophytes we see the endowments of simple vegetable cells.
A piece of bioplasm, or living tissue, transforms its outer layer into
cellulose, and forms chlorophyll or starch in its interior, absorbing
new pabulum continually, and casting off the old effete atoms. The
relationship of each family is seen by these functions common to all.
Each species of each family has, however, its own peculiarities, which
distinguish it from all others. The Protococci remain rounded cells, but
the Oscillatoria, Confervaceæ, etc., have an instinct for elongation, so
that they become tubular, and for distributing endochrome in
characteristic spiral patterns, varying in each species, while the
Diatoms appropriate silica from their pabulum to harden the cellulose
envelope, and arrange it in their frustules atom by atom, each species
after its own pattern, and all with marvelous regularity and beauty. The
Monistic theory of the universe has no satisfactory reason to give for
the existence of such varied tendencies. Schleiden has well said, “We
do, indeed, see into the mechanism of the puppet; but who holds the
strings and directs all its motions to _One Purpose_? Here closes the
office of the naturalist; he turns from the world of space and lifeless
matter upward to where, in holy anticipation, we seek the Ruler of
worlds.”[18]
CHAPTER VII.
T H A L L O G E N S .
Thus Nature varies; man and brutal beast,
And herbage gay, and silver fishes mute,
And all the tribes of heaven, o’er many a sea,
Through many a grove that wing, or urge their song
Near many a bank of fountain, lake, or rill,
Search where thou wilt, each differs in his kind,
In form, in figure differs.—LUCRETIUS.
1. THALLUS-PLANTS, called also Thallogens, or Thallophytes, (from
_thallos_, a frond, or green leaf; _genein_, to produce, _phyton_, a
plant,) have no true vascular system, but are composed of cells of
various sizes, forming membranous expansions, or filaments more or less
simple, branched, or interlacing. They differ from Protophytes by the
more intimate union of cells in their structure. In some of the
Protophytes there is an adhesion of the cells by a fusion of their
gelatinous investment, yet each cell is a repetition of the former one,
and is capable of living independently if detached, so that each answers
to the designation of a unicellular, or single-celled plant. In the
Thallogens the cells are not only closely united, but exhibit a
differentiation in structure or function, and a relation of mutual
dependence, constituting each plant (not each cell) an individual.
2. The higher _Algæ_, or Sea-weeds, the _Lichens_, and the _Fungi_ may
be regarded as Thallophytes, although some species may present many
points of resemblance with the simple Protophytes.
3. The ALGÆ, or Sea-weeds, have been divided into three orders, the Red,
the Olive, and the Green Sea-weeds—Rhodospermeæ, Melanospermeæ, and
Chlorospermeæ. The latter order generally includes the Confervoid and
other families which we have considered as unicellular plants. When we
examine the higher Sea-weeds, we find a certain foreshadowing of the
distinction between Root, Stem, and Leaf, which is characteristic of
still higher types. This sort of unconscious prophecy of higher forms to
come is by no means uncommon in other classes both of plants and
animals, and affords another proof that living things have been formed
on an intelligent plan. In the Sea-weeds, however, the apparent
distinction of stem and root serves for little else than the mechanical
attachment of the plant. There is no departure from the cellular type,
the only modification being that the layers of cells are of different
sizes and shapes.
[Illustration: FIG. 35.—Section of receptacle
of _Fucus platycarpus_, lined with filaments
containing antheridial cells and sporangia. ]
4. The Olive Sea-weeds, or Fucoids, (_Melanospermæ_,) often grow to a
considerable size, attached by sucker-like roots to the rocks, and, in
some cases, buoyed up by air-bladders. Others are parasitical. The
fructification of many species in this group is sexual. In the common
bladder-wrack, _Fucus vesiculosus_, the reproductive organs are on
different plants, but in other species, as _Fucus senatus_, they are
both together, the one olive-green, the other orange-yellow. The
“receptacles” are at the extremities of the fronds, and may be known to
be mature by each discharging little gelatinous masses adhering round
its orifice. If now a section is made through it, it will be seen to be
a cavity lined with filaments, some of which project through the pore.
The filaments, or _antheridia_, are chains of cells containing
_antherozoids_. These are yellow oval bodies, with two thread-like
appendages, which, when liberated by the bursting of the cell, have a
spontaneous and rapid motion around the _sporangia_, (or parent cells of
the germs,) which they fecundate. These sporangia are pear-shaped bodies
lying near the walls of the Cavity, or receptacle, and each one
produces, by fission, a cluster of eight cells, or octospores. (Fig.
35.)
5. Among the red Sea-weeds, or _Rhodospermeæ_, are various simple but
beautiful forms, eagerly sought for by sea-side collectors for albums.
They live generally in deeper water than other sea-weeds, and show their
richest tints when growing in the shade. The genus _Polysiphonia_
contains many species, some small and delicate, or long and filmy, and
of various tints of brown or violet. The fronds are thread-like and
jointed; the joints striped, since the stem is composed of parallel
tubes or siphons, from whence its name, (_poly_, many; _siphon_, tube.)
The fructification is twofold, on distinct plants: 1.) _Ceramidia_, or
urn-shaped cells containing pear-shaped spores; 2.) _Tetraspores_, or
groups of four spores, imbedded in swollen branchlets. The genus
_Ceramium_ is thread-like, jointed, branched, with repeated forkings.
The tips of the filaments are always forked, and often curl toward each
other. The fruit is of two kinds: 1.) Berries, or capsules, containing
seeds, and called _favellæ_. 2.) Tetraspores, or groups of four seeds,
immersed in the substance of the branch, and surrounding it in a whorl.
Another beautiful and not uncommon genus, found at low-water mark, or
cast up after a storm, is _Ptilota_, (from a Greek word signifying
“pinnated.”) It has many small branches, or pinnæ, and these again are
cut into smaller divisions, or pinnula. At the top of the latter is the
fructification, consisting of minute capsules, or _favellæ_. Some plants
also contain tetraspores. _Corallines_ are a family of red Sea-weeds
whose tissue is consolidated by calcareous deposit. The arrangement of
tetraspores in the red Algæ is illustrated by Fig. 36.
[Illustration: FIG. 36.—Arrangement of tetraspores, in _Carpocaulon
mediterraneum_: A. Entire plant. B. Longitudinal section of branch. (N.
B. Where only three tetraspores are seen it is merely because the fourth
did not happen to be so placed as to be seen at the same view.) ]
6. The class of LICHENS consists of cellular plants of very simple
structure. They form irregular patches, generally dry, upon stones,
trees, etc., which they decorate with various colors. They are found in
all climates. Some are used in medicine, as the Iceland Moss, (_Cetraria
Islandica_;) others, as the Orchil, produce a valuable dye, and one
species, _Leonora esculenta_, found in the Desert of Tartary, seems to
fall from the sky as a miraculous manna. Men and beasts may be nourished
on it. It is in the form of globules, varying from the size of a pin’s
head to that of a hazel nut; and as it grows freely, not being attached
to any substance, it is readily driven by the wind from one place to
another.
The thallus of Lichens may be of various sizes, forms, and colors. (Fig.
37.) Its fruit is called _Apotheceia_, and forms cups, or shields, of
various forms, often colored bright red, yellow, gray, or black. When
these are divided by vertical sections they are found to contain a
number of _asci_, or spore-cases, arranged vertically among filaments
which are termed _paraphyses_. The fecundating apparatus is called the
_Spermogonia_, and consists of small rounded or oblong organs, lodged in
particular tubercles or immersed in the superficial layers of the
thallus. The cellular filaments of the spermagonia give off minute oval
bodies, called _spermatia_, which are analogous to the antherozoids of
Algæ, but differ in being destitute of spontaneous motion.
[Illustration: FIG. 37.—Lichens. _a._ Cladonia, with scarlet
conceptacles. _b._ Usnea. _c._ Sticta. _d._ Parmelia. _e._ Vertical
section of receptacle. _f._ Same highly magnified, with thecæ and
paraphyses. _g._ Double spore. ]
7. The FUNGI form an extensive class of primitive organisms, generally
ranked as plants, but which have so many peculiarities as to entitle
them to be considered apart. We should not greatly err if we regard them
as a third type of living things, differing both from animals and
vegetables. They have no chlorophyll, as green vegetables have, and
which enables them to break up carbonic acid. (Chap. VI, Sec. 2.) Light
is not essential to the activity of Fungi, as it is to that of
vegetables. They are incapable of assimilating inorganic food, but live
upon organic substances. They are the agents of fermentation and of
putrefaction, and their principal office seems to be to break down and
to restore to the inorganic world the effete formed material of animal
and vegetable life. Mushrooms, Puff-balls, Molds, and the Rust of grain
are examples of Fungi.
8. The simplest forms of Fungi resemble Protophytes, except in the
absence of chlorophyll, either green or red. Recent investigations have
indicated that those which seem most simple are but imperfectly
developed states of other species. The _Torula cerevisiæ_, or
yeast-plant, which is the cause of fermentation in solutions of sugar,
and _Bacteria_ (Fig. 38) of various forms, which cause putrefaction in
animal substances, appear to be varieties, or stages, in the development
of some of the “molds,” or microscopic fungi, many of which are capable
of polymorphism, or the assumption of many forms. In some kinds of fungi
the bioplasm shows amœboid movements, having a great resemblance to some
of the lower forms of animal life.
[Illustration: FIG. 38.—Appearances presented by Bacteria under the
microscope. At _c_, are isolated Bacteria; at _d_, they are arranged
round a center; while at _a_ they appear in long strings; at _e_ is
observed a solitary torula. All highly magnified. ]
9. Fungi are cellular organisms of variable consistence. They exhibit
two well-defined structures, a _mycelium_, or spawn, (Gr. _myces_, a
fungus,) formed of filaments sometimes assuming a membraneous, a
tubercular, or a pulpy form, and a _fruit_, or reproductive structure,
which differs in different tribes. The essential reproductive organs are
spores, called also _conidia_, usually four, or some multiple of four,
attached to the cellular tissue, and supported on simple or branched
filaments, (called _conidiophores_, or _basidia_,) or contained in sacs,
(_thecæ_, _cystidia_, or _asci_; all of which words, derived from the
Greek, have similar meaning.)
10. Fungi have been divided into six orders, as follows:
1.) _Hymenomycetes_, (Gr. _hymen_, a membrane, and _myces_, a fungus.)
Mycelium inconspicuous, bearing fleshy fruits which expand so as to
expose the spore-bearing membrane to the air. Mushrooms are well-known
examples.
2.) _Gasteromycetes_, (Gr. _gaster_, belly.) Fructifying surface
inclosed, as in Puff-balls.
3.) _Coniomycetes_, (Gr. _konis_, powder.) The spawn or vegetative part
is reduced to a minimum, and the abundant spores form a dusty or
sometimes a gelatinous mass. The rust and bunt of wheat and other grains
are instances.
4.) _Hyphomycetes_, (_hyphao_, to weave.) The vegetative part consists
mostly of loose threads, as the naked seed Molds.
5.) _Ascomycetes_, (_askos_, a bag.) The sacs, or asci, containing the
sporidia are either packed into an exposed hymenium, or line the
interior of the fruit-bearing cysts, as Truffles, etc.
6.) _Physomycetes_, (_physa_, a bladder.) Mycelium filamentous, bearing
sacs, containing minute sporules, as the common Bread-mold.
11. The difficulty of determining what forms are to be regarded as
species, and what as mere varieties, finds many illustrations in the
class of Fungi. We know but little of the influence of external
conditions in modifying forms, and the forms of fungi are so exceedingly
unstable that the best observers are often at a loss. Yet this
variability is only one of degree, since all living beings are more or
less subject to modifications of form by external influences. It is this
variability which has rendered the Darwinian hypothesis of evolution by
“the survival of the fittest” so plausible a theory. But notwithstanding
this capability of modification, there is still a certain fundamental
and specific type for each assemblage of forms, and the amount of
variability is strictly limited.
12. Many diseases of plants and animals are associated with the growth
of Fungi. The “mildew” (_Puccinia_) and “rust” (_Uredo_) of wheat, etc.,
the potato blight, (_Peronospora_,) the disease in Silk-worms called
Muscardine, (_Botrytis_,) the false membrane in diphtheria, the white
patches in aphthæ, or thrush, and many skin affections, afford examples.
Pyæmia is supposed to result from _bacteria_ in the blood, and many
epidemic diseases have been ascribed to similar origin. The prevalence
of atmospheric changes, however, and variations in external conditions,
as light, heat, moisture, etc., have much to do in predisposing both
animal and vegetable tissues to disease, and in producing epidemics.
Since the office of Fungi is to remove decaying or effete organic
matter, we must discriminate between those diseased conditions which
provide a habitat for fungi and the effects produced by the fungi
themselves.
13. The excessively minute and almost vapor-like sporules of fungi float
about in the atmosphere in countless numbers, only waiting for a fitting
soil in which to grow. As long as there is no refuse matter to be
removed these scavengers are unemployed, but the smallest quantity of
decaying animal or vegetable matter left exposed becomes covered with
spores, which develop with astonishing rapidity. A scanty number of
spores, only to be detected by careful research, will in a few days, and
sometimes in a single night, give birth to myriads, to repress or remove
the nuisances referred to. When the offal diminishes fewer of the spores
find soil on which to germinate, and when all is consumed the active
legions return to their latent or undeveloped state. Like Milton’s
spirits—
So thick the aëry crowd
Swarmed and were straitened; till, the signal given,
Behold a wonder; they but now who seemed
In bigness to surpass earth’s giant sons,
Now less than smallest dwarfs.
14. In the chapter on the Protophyte type of vegetable life, we
considered the bioplasm, or living matter, differing in each kind, yet
agreeing in one particular, namely, that each cell exhibits a repetition
of the form and power of the parent-cell. In the Thallogens we find
another idea predominating, or rather two leading ideas, the
co-ordination of many cells in the structure of one individual, and the
differentiation of cells in form and function, analogous to the division
of labor in human society. Respecting the first, Joseph Cook has well
remarked, in his axiomatic style: “Living tissues are co-ordinated
according to definite plans. As every change must have an adequate
cause, we are compelled to infer the existence of a co-ordinating force
behind the action of the bioplasts in each organism. That force is the
cause of form in organisms. It has as many types as there are types of
organisms, vegetable and animal.”[19] The same subtle power which
co-ordinates, also differentiates the cells. This power resides in the
original germ, before the organization of the individual form, and is
what we have already defined as Life, and is not explicable by physical
causes. “Collocation of parts in an organism is precisely what
materialism has never yet explained.”[20]
CHAPTER VIII.
A C R O G E N S .
Flower in the crannied wall,
I pluck you out of the crannies,
Hold you here in my hand,
Little flower, root and all,
And if I could understand
What you are, roots and all, and all in all,
I should know what God and man is.
—TENNYSON.
1. In the type of Acrogens the instinct of development, or evolution of
cells, is seen only at the summit or apex of the stem. Cells in other
parts of the plant may enlarge, but do not multiply themselves. These
plants generally have distinct stems and leaves, with stomata, (Chap.
IV, Sec. 11,) a certain amount of vascular tissue, (Chap. IV, Sec. 10,)
and _thecæ_, or cases containing spores. The Stoneworts, (_Characeæ_,)
the Liverworts, (_Hepaticæ_,) the Horsetails, (_Equisetaceæ_,) the
Ferns, (_Filices_,) and the Mosses, (_Musci_,) are the principal
families of Acrogens.
2. The Stoneworts (CHARACEÆ) have generally been regarded among Algæ, or
water-weeds. But they differ greatly from Algæ in having a distinct axis
of growth, and appendages. The axis may be a simple tube, (Genus
_Nitella_,) or a tube with a cortical layer of smaller tubes surrounding
it, (Genus _Chara_.) They are found in ponds and rivers, in tangled
masses of a dull green color. Each plant is hardly thicker than a stout
needle, but may be three or four feet long. It has rootlets springing
from the axis, by which it is fixed in the muddy bottom of the stream,
etc., but the main source of its nutriment is the water in which it
lives. It possesses chlorophyll, and in consequence decomposes carbonic
acid under sunlight, retaining the carbon to form part of its own
substance, and giving off the oxygen. The branchlets (or _leaves_, as
they are called) are grouped in whorls, or spring from the same height
in the stem, and at regular intervals. (Fig. 39.) The main stem is
called the axis, and a branch, when it exists, is a secondary stem. The
appendages are the leaves, branches, rootlets, and reproductive organs.
The points on the axis, or stem, from which the appendages spring, are
called _nodes_, the intervening parts being the _internodes_. In Chara
the internodes have a spiral striation. Growth takes place at the apex
by the development of new nodes and internodes. Each internode is formed
by the growth and elongation of one cell.
[Illustration: FIG. 39.—_Nitella flexilis_: A. Stem and branches of the
natural size. _a._ _b._ _c._ _d._ Four verticils of branches issuing
from the stem. _e._ _f._ Subdivision of the branches. B. Portion of the
stem and branches enlarged. _a._ _b._ Joints of stem. _c._ _d._
Verticils. _e_. _f._ New cells sprouting from the sides of the branches.
_g._ _h._ New cells sprouting at the extremities of the branches. ]
[Illustration: FIG. 40.—Growing Point of Chara. _a._ Terminal cell
dividing. _b._ Cells forming youngest node, and which by their fission
will give rise to a whorl of appendages. _c._ _c._ Internodal cells.
_d._ Incipient appendages. _e._ Same farther advanced. _f._ _f._
Terminal cell dividing. ]
The terminal bud is formed by a single cell, which divides by fission
into two, one of which forms the internode, while the other subdivides
into lateral cells, which, by division, produce the appendages. In the
latter, after a certain stage, the terminal cell is incapable of further
division, but in the stem the process continues indefinitely. (Fig. 40.)
The reproductive organs in these plants are of two kinds, oval
_sporangia_, or spore-fruits, and _antheridia_. The latter are smaller
than the sporangia, and globular, and contain filaments whose cells are
changed into little ciliated bodies called _antherozoids_. (Fig. 41.)
The growing spore from the sporangium gives off two filaments resembling
the hyphæ in fungi, one of which serves as a temporary root, and a cell
in the other produces a group of lateral projections from which the
young Chara springs. This temporary structure is termed the
_pro-embryo_.
[Illustration: FIG. 41.—Portion of Antheridium of Chara. 1. Several
jointed filaments attached to a vesicle. 2. End of one of the tubes, a
spiral thread escaping. 3. A tube nearly empty. 4. An antherozoid with
its cilia. ]
In _Chara vulgaris_ the circulation, or movement, of bioplasm in
vegetables was first discovered. (Chap. II, Sec. 7, and Chap. IV,
Sec. 6.)
3. The Liverworts, or HEPATICÆ, form a class or group of plants
generally considered intermediate between Lichens and Mosses. They are
furnished with leaves, or lobed fronds, with rootlets on the under
surface, which send up stalks carrying either round, shield-like disks,
bearing _antheridia_, or radiating bodies, bearing at first
_archegonia_, or female organs, and afterward _sporangia_, or
spore-cases. (Fig. 42.)
[Illustration: FIG. 42.—Frond of _Marchantia polymorpha_, with
gemmiparous conceptacles, and lobed receptacles bearing pistillidia. ]
The arrangement of the stomata, or breathing pores, in these humble
plants is far more complex than we find it in others. The leaves of all
the higher plants have cavities, or air-spaces, communicating with the
external world by openings, or pores, which are guarded by elastic
cells; but in _Marchantia polymorpha_ the green surface of the frond is
seen by a low magnifying power to be divided into diamond-shaped spaces,
containing an opening in each. On making a thin section, as in Fig. 43,
each of these stomata will be seen to form a sort of shaft, or chimney,
of four or five rings, or courses, of cells, the lowest ring regulating
the aperture into the leaf-grottoes below.
[Illustration: FIG. 43.—A. Portion of frond of _Marchantia polymorpha_
seen from above. _a._ _a._ Lozenge-shaped divisions. _b._ _b._ Stomata
seen in the center of the lozenges. _c._ _c._ Greenish bands separating
the lozenges. B. Vertical section of the frond, showing _a._ _a._ the
dense layer of cellular tissue forming the floor of the cavity _d._ _d._
_b._ _b._ Cuticular layer, forming its roof. _c._ _c._ Its walls. _f._
_f._ Loose cells in its interior. _g._ Stoma divided perpendicularly.
_h._ Rings of cells forming its wall. _i._ Cells forming the obturator
ring. ]
The spores of Marchantia are attached to _elaters_, or spirally-coiled
elastic fibers, whose extension scatters the spores.
3. The EQUISETACEÆ, or Horsetails, are found in most parts of the world,
save Australia and New Zealand. They generally grow in wet places,
sending up shoots from a creeping stem, or _rhizome_. The cuticle is
remarkable for the great quantity of silica contained in it. The
particles of this mineral, each having a double axis of refraction, are
arranged in rows parallel to the axis, and are beautiful objects under
the microscope, with polarized light. The abundance of silica has led to
some of these plants being used as natural files for polishing various
articles.
[Illustration: FIG. 44.—_a._ Equisetum arvense. _b._ Equisetum
sylvaticum. _c._ Section of the spike. _d._ A sporange. _e._ A spore
with its elaters coiled. ]
The shoots are jointed, each articulation having a toothed membraneous
sheath, and having whorls of branches and branchlets. The fructification
is in the form of terminal cones, with scales bearing spore-cases, and
opening by a longitudinal fissure. Each of the spores has a pair of
spiral filaments, with clubbed ends, and attached by their center, so as
to look like four stamens. (Fig. 44.)
4. FERNS in tropical countries are sometimes rivals of the most
beautiful Palms, having trunks varying from two or three to sixty or
eighty feet in height, formed of the consolidated bases of the fronds.
In these Tree-ferns the fronds are either repeated in whorls, or they
form a tuft at the summit, constituting in the latter case a collection
of whorls with suppressed internodes. In the ordinary ferns, or brakes,
of temperate climes, the stem is an underground one, or _rhizome_, and
the disposition of the fronds is seldom observed.
The epidermis of the stem is of a brownish hue, and the general cellular
structure, or _parenchyma_, consists of many-sided nucleated cells,
containing chlorophyll and starch granules. There are also vessels
(annular, spiral, and scalariform, or ladder-like) and fibrous or woody
tissue, forming together the _sclerenchyma_, or harder tissues. (Chap.
IV, Secs. 6 to 10.)
[Illustration: FIG. 45.—Diagram, showing the mode of growth in the stem
of a Fern. A. B. C. Stems of ferns showing successive stages of growth.
_a. a. a._ Terminal cells, the latter just after being produced by
division. _b._ A cell which will give rise to an internode. _c._ Shows a
ring or cluster of cells giving rise to a node. _d._ Epidermal cells.
_e._ Parenchyma. _f._ Sclerenchyma. _g._ Scalariform vessels. _h._
Spiral vessels. _k._ An appendage, originating at the node. _d._ _e._
_f._ _g._ and _h._ all arise from the multiplication and metamorphosis
of the “growing” cells. ]
In Fig. 45 the acrogenous growth of a fern is illustrated, together with
the metamorphosis of the terminal cell into the various tissues. In
flowering plants the terminal cell of the leaf-bud becomes barren, and
the enlargement of the leaf depends on the multiplication and growth of
cells nearer the base; but in the fern the leaf-bud grows as the stem
does, so that the peduncle is first formed, then the embryo leaf, then
the pinnules, etc.
Underneath the frond of a fern we may sometimes see little brown
patches. Each patch is a _sorus_, (sometimes covered by a membrane
called an _indusium_,) and the little brown bodies constituting it are
_sporangia_, or spore-cases, which have been developed from epidermal
cells. An elastic ring (_annulus_) surrounds each sporangium, and
assists in opening it. The growth of these minute spores may be observed
by sowing them on a saucerful of fine mold, covering with a bell-glass
or tumbler, and keeping it moist, warm, and shaded. A green film will
spread over the soil, which can be taken up, from time to time, on the
point of a knife for microscopic examination. The little spore swells
and bursts, and throws out a rootlet which gets its nourishment from the
soil. Then a number of delicate cells are formed from the mother-cell in
the spore, making a little green scale, (the _prothallium_,) which
throws out rootlets on its under side. This prothallium produces two
kinds of cells, one set called _antheridia_, which contain spiral
filaments which escape to enter the others, called _archegonia_, or
germ-cells, from which the future fern is reproduced. (Fig. 46.)
The fossil remains of Ferns in the various strata of the earth’s crust
are very numerous, especially in the Coal measures. These deposits
exhibit the remains of many species now extinct. Immense tree-ferns and
gigantic Lycopodiaceæ (Club-mosses) flourished in an atmosphere charged
with moisture and carbonic acid gas, which, by plant assimilation and
liberation of oxygen, is thought to have been purified and prepared for
the use of successive tribes of animals and of man.
5. MOSSES are minute and lowly plants, but they are by no means
insignificant. There are about ten thousand species, some of which are
not over a hundredth part of an inch in height, while others are several
inches high. Mosses have a distinct axis of growth, and the delicate
leaves are arranged with great regularity. The stem shows some
indication of the separation of a cortical, or bark-like portion, from
the medullary, or pith-like, by the intervention of a circle of bundles
of elongated cells, from which prolongations pass into the leaves, so as
to afford them a sort of midrib.
[Illustration: FIG. 46.—Ferns and their parts. _a._ Fronds and
root-stalk. _b._ Frond, showing the spore-cases. _c._ Exterior and
interior of seed-vessel. _d._ Fronds, gradually unfolding. _e._ A Theca,
or spore-case, before opening. _f._ A Theca, or spore-case, discharging
its spores. _g._ Prothallus of its natural size. _h._ Lower surface of
prothallus, much enlarged, showing the organs whose reciprocal action
determines the development of the fern. _i._ Various forms of one of
these organs when in movement. _j._ Inclosed vesicle, in which the
development of the fern commences.]
The root-fibers are long tubular cells, quite transparent, within which
the circulation of the bioplasm may be seen. Dr. Hicks has observed
portions of the inclosed bioplasm detached, and having amœboid motions.
The stems of Mosses usually terminate in filaments, or foot-stalks,
supporting an urn-shaped vessel closed by a lid, (_operculum_,) which is
covered by a cap, or hood, (_calyptra_.) Under the operculum, the edge
of the urn is a beautiful toothed fringe, (the _peristome_,) and within
the urn, or spore-capsule, (_sporangium_,) are double-coated spores.
(Fig. 47.)
[Illustration: FIG. 47.—Structure of Mosses. A. Plant of _Funaria
hygrometrica_, showing, _f._ the leaves; _u._ the urns supported upon
the setæ, or footstalks, _s_, closed by the operculum, _o_, and covered
by the calyptra, _c._ B. Urns of _Encalyptra vulgaris_, one of them
closed and covered with the calyptra, the other open. _u._ _u._ The
urns. _o._ _o._ The opercula. _c._ Calyptra. _p._ Peristome. _s._ _s._
Setæ. C. Longitudinal section of very young urn of _Splachnum_. _a._
Solid tissue forming the lower part of the capsule. _c._ Columella. _l._
Loculus, or space around it for the development of the spores. _e._
Epidermic layer of cells, thickened at the top to form the operculum,
_o._ _p._ Two intermediate layers, from which the peristome will be
formed. _s._ Inner layer of cells forming the wall of the loculus. ]
In developing into new plants, the outer coat of the spore bursts and
the inner wall protrudes. New cells grow from the extremity, forming a
filament, whose cells at certain points multiply by subdivision, so as
to form rounded clusters, like the prothallus of Ferns, or the
pro-embryo of Chara, from each of which an independent plant may arise.
The urn, or capsule, is not the real fructification of a moss, but its
product, since Mosses, like Liverworts, etc., possess both antheridia
and pistillidia, although they are often inconspicuous. They are found
either together, or on different parts of the same plant, or on
different plants. They are usually situated at the bases of the leaves,
close to the axis. The _antheridia_ are globular or elongated capsules
containing sperm-cells, each of which produces a moving antherozoid,
which escapes at the summit of the capsule. Hair-like filaments
(_paraphyses_) around the antheridia are considered to be sterile or
undeveloped antheridia. The _archegonia_ are like those of the
Hepaticeæ, and when fertilized the embryo-cell develops by cell-division
into a conical body elevated upon a stalk. This tears the walls of the
flask-shaped archegonium by a circular fissure, carrying the upper part
as the _calyptra_, or hood of the “urn,” while the lower part remains as
a sort of collar around the stalk.
6. The characteristics of the type of Acrogens are the growth of cells
at the summit only; the appearance of a distinct cortical portion, or
epiderm, and of vascular and fibrous tissue; and a sort of alternation
of generations in the provision of a prothallus, so that plants of this
type may not improperly be designated Prothallus plants, as the higher
types are sometimes known as Monocotyledonous, or Dicotyledonous plants.
7. As an illustration of the reflections natural to a well-regulated
mind from the study of natural objects, even of minute and apparently
insignificant Acrogens, an incident in the life of Mungo Park is
appropriate. This enterprising traveler, during one of his journeys into
the interior of Africa, was robbed and stripped by banditti. When the
robbers had left him, he says: “I sat for some time looking around me
with amazement and terror. Whichever way I turned, nothing appeared but
danger and difficulty. I found myself in the midst of a vast wilderness,
in the depth of the rainy season, _naked_ and _alone_, surrounded by
savage animals, and men still more savage. I was five hundred miles from
any European settlement. All these circumstances crowded at once upon my
recollection, and I confess that my spirits began to fail me. I
considered my fate as certain, and that I had no alternative but to lie
down and perish. The influence of religion, however, aided and supported
me. I reflected that no human prudence or foresight could possibly have
averted my present sufferings. I was indeed a stranger in a strange
land, yet I was still under the protecting care of that Providence who
has condescended to call himself the stranger’s friend. At that moment,
painful as my reflections were, the extraordinary beauty of a small moss
irresistibly caught my eye, (I mention this to show from what trifling
circumstances the mind will sometimes derive consolation,) and, though
the whole plant was not larger than the top of one of my fingers, I
could not contemplate the delicate conformation of its root, leaves, and
fruit without admiration. Can that Being (thought I) who planted,
watered, and brought to perfection, in this obscure part of the world, a
thing which appears of so small importance, look with unconcern upon the
situation and sufferings of creatures formed after his own image? Surely
not. Reflections like these would not allow me to despair. I started up;
and, disregarding both hunger and fatigue, traveled forward, assured
that relief was at hand, and was not disappointed.” Such views of the
universe and of its Creator infuse strength into the human soul, and
give a vigor to human character which is impossible otherwise. For the
good-ordering of human life they are infinitely above all Monistic
speculations and theories of Evolution, which belittle or lose sight of
the individual in a romantic sentiment respecting primordial and
progressive development of all.
CHAPTER IX.
E N D O G E N S .
What time this world’s great workmaister did cast
To make all things such as we now behold,
It seems that He before His eyes had plast
A goodly patterne, to whose perfect mould
He fashioned them as comely as he could,
That now so fair and seemly they appear
As naught may be amended anywhere.
—SPENSER.
1. ENDOGENOUS plants have no separable bark, nor distinct concentric
circles in the stem. Their fibro-vascular bundles, consisting of spiral
and porous vessels and woody fibers, descend from the leaves downward,
converging at first toward the center, but afterward diverging outward
until they reach the roots, or attach themselves to the hardened tissue
of the outer or cortical layer, corresponding to the bark in Exogens,
but harder than the rest of the stem, and inseparable from it. It used
to be thought that the woody portion was added to the center, and pushed
the first-formed fibers toward the circumference; hence the term
Endogenous, (_endon_, within, and _gennao_, to produce.) In strict
scientific accuracy the term only applies to the fibers at the early
part of their course, since in the latter part they become blended in
the cortical layer, forming a tough net-work. The center of the stem
when young is filled with cells which sometimes disappear, except at the
nodes, leaving the stem hollow, as in Grasses.
[Illustration: FIG. 48.— Endogenous Leaf, showing parallel venation. ]
The embryo of Endogens has but a single _cotyledon_, or seed-lobe, on
which account they are often termed Monocotyledons. Acrogens have no
seed-lobe, but cellular spores, and are called acotyledons, (from the
Greek α, privative, and _kotyledon_, something hollow,) while Exogens
have two seed-lobes, and are dicotyledons.
The veins in the leaves of Endogens are generally parallel, or straight,
(Fig. 48,) and do not form a net-work, and the parts of the flower are
arranged in sets of threes, or of some multiple of three.
2. Exceptions to the parallel venation of leaves in Endogens have been
placed by Lindley in a class by themselves—the _Dictyogenæ_, (from
_dictyon_, a net, and _gennao_, to produce;) in allusion to the
reticulation of the leaves. They comprise the Yam tribe,
(_Dioscoreaceæ_,) the Sarsaparilla family, (_Smilaceæ_,) and the
Trillium family, (_Trilliaceæ_.) The other classes or sub-classes are,
1. _Petaloideæ_, or _Floridæ_, in which the flowers consist either of a
colored perianth (a floral envelope) or of scales arranged in a whorl.
2. _Glumiferæ_, in which the flowers have imbricated bracts or scales,
called _glumes_. This includes the two orders of grasses and sedges. The
_Petaloideæ_ are divided into three sections: 1. _Epigynæ_, having
perfect flowers, and a superior perianth, (ovary inferior,) as Orchids,
Gingers, Irids, Amarylids, etc.; 2. _Hypogynæ_, having perfect flowers
and an inferior perianth, (ovary superior,) as Lilies, Rushes, and
Palms; 3. _Incompletæ_, with imperfect flowers, without a proper whorled
perianth, as Screw-pines and Arums.
3. GRAMINEÆ, the Grass Family, is one of the most important orders in
the vegetable kingdom, whether we regard it as supplying food for man or
herbage for animals. Grasses are found in all quarters of the globe, and
are said to form about 1-22d part of known plants. There are about 4,000
species, and their structure is the most simple of the higher forms of
vegetation. Their stems form protecting sheaths to the growing shoots,
and have alternate leaves. Their flowers, or glumes, present many
varieties, producing the distinctive characters of families or tribes,
and genera. Among the grasses are the nutritious cereal grains, as
Wheat, (_Triticum_,) Oats, (_Avena_,) Barley, (_Hordeum_,) Rye,
(_Secale_,) Rice, (_Oryza_,) Maize or Indian Corn, (_Zea_,) etc. Here,
also, are found various pasture grasses, as Rye-grass, (_Lolium_,)
Timothy-grass, (_Phleum_,) Meadow-grass, (_Poa_,) etc. (Fig. 49.)
[Illustration: FIG. 49.—Wheat, Barley,
Meadow-grass. ]
The cereal grains have been so generally distributed by man that all
traces of their native country are lost. They seem to be examples of
permanent varieties or races preserved by cultivation.
The grains, or seeds, of many kinds are used for food, since they
contain a large amount of starch and gluten. Sugar is also obtained from
many grasses, as the Sugar-cane, (_Saccharum officinarum_,) Sweet
Sorghum, (_Sorghum saccharatum_,) etc.
Grasses contain a large quantity of silicious matter in the epidermis of
their stalks, which sometimes accumulates in the joints, as the
Tabasheer in the joints of Bamboo, (_Bambusa_.) This latter is a
tree-like grass, sometimes growing fifty or sixty feet high. It is
applied to an almost endless variety of purposes. The Chinese use it, in
one way or other, for nearly every thing they require. The sails of
their ships, as well as their masts and rigging, and articles of
furniture, as mats, screens, chairs, tables, bedsteads, and bedding, are
all made out of the Bamboo, which is cultivated with great care.
The stems of some grasses run under-ground, and are useful in
consolidating the sand of the sea-shore. This property renders some
grasses (as _Triticum repeus_) difficult to exterminate.
4. SEDGES, (_Cyperaceæ_,) are grass-like herbs, with angular stems and
narrow, tapering leaves wrapping round the stem, but without the
slitting sheath. Their flowers are borne on bracts, or scales, united in
an imbricated manner so as to form a spike. In Lapland they equal the
grasses in number, but the proportion decreases toward the equator. Few
plants of this family are attractive to the eye, but many of them are
useful. The creeping stems of _Carex arenaria_ bind the shifting sands
on the shores of Brittany and Holland into a wind-defying mass. The
_Papyrus antiquorum_ of the Nile (the Bulrush of Scripture) belongs to
this family. It formerly furnished the world with paper, besides being
used for making boats, ropes, etc. (Fig. 50.)
[Illustration: FIG. 50.—The Papyrus of the Nile. ]
[Illustration: FIG. 51.—Cocoa-nut Tree,
(_Cocos nucifera_,) and Plantain,
(_Musa Paradisiaca_.) ]
5. Linnæus, the great Botanist, called Grasses the plebeians, and PALMS
the princes, of the vegetable world. The latter are for the most part
trees of gigantic growth, often reaching dimensions unknown among other
plants. They are used for supplying food and for forming habitations.
The fruit of some is edible, while that of others is hard. Many supply
oil, wax, starchy matter, and sugar, which is fermented to form an
intoxicating beverage. Their fibers make ropes, and the reticulum about
their leaves is sometimes manufactured into brushes.
The Date palm, (_Phœnix dactylifera_,) which supplies food to so many of
the inhabitants of Arabia and Africa, is considered to be the Palm of
the Bible. The Cocoanut palm (_Cocos nucifera_) is one of the most
useful, supplying the South Sea Islander with food, clothing, houses,
utensils, ropes, oil, sugar, wine, and Palm cabbage from the terminal
bud, etc. (Fig. 51.)
Sago and other starchy matter is obtained by bruising and washing the
cellular tissue of many Palms, especially _Sagus Rumphii_, _S. lævis_
and _S. genuina_.
6. The BANANA family (_Musaceæ_) contains plants which furnish a large
supply of nutritious fruit, while their leaves afford valuable fibers.
The best known species are _Musa paradisiaca_, or Plantain, and _M.
sapientum_, or Banana, (Fig. 52;) the former a denizen of the Old World,
and the latter of the New. The specific name of the first originated in
a notion of some of the old botanists that it was the forbidden fruit of
Eden. A quaint writer remarks that it is not likely that a plant so
useful should have been the forbidden fruit. The Banana supplies the
inhabitants of the tropical islands with wholesome and abundant food,
pleasant drink, valuable medicine, materials for clothing, baskets,
mats, and with almost all other necessaries of their simple life. _Musa
textilis_ supplies a flax-like fiber, from which some of the finest
Indian muslins are made.
[Illustration: FIG. 52.—Banana, (_Musa sapientum_.) ]
7. The ARROW-ROOT family, (_Marantaceæ_,) the PINEAPPLE family,
(_Bromeliaceæ_,) and the GINGER family, (_Zingiberaceæ_,) contain many
useful species of Endogens. Here also are classed many of the showy
flowers of our gardens and hot-houses. The IRIS family, (_Iridaceæ_,)
containing the Iris, Gladiolus, and Crocus, etc.; the singular aquatic
plants of the Hydrocharidaceæ, as Hydrocharis and Valisneria; and the
AMARYLLIS family, (_Amaryllidaceæ_,) embracing the Daffodil, Amaryllis,
and Agave, are of this class. The last-named plant is sometimes called
the American Aloe, (_Agave Americana_,) and, according to gardening
fable, only blooms once in a hundred years, hence called Century plant.
Its large, hard, spinous leaves grow slowly for years, when suddenly, in
the course of a single season, a stem shoots up forty or fifty feet in
height, bearing a crest of flowers. In Peru and Mexico an intoxicating
beverage called _pulque_ is made from the sap.
[Illustration: FIG. 53.—Orchids, (_Orchidaceæ_.) ]
8. The ORCHID family (_Orchidaceæ_) exhibit the greatest variety of
forms and brilliancy of color among all the vegetable tribes. The
flowers often resemble insects, as butterflies, moths, flies, and
spiders; or birds, as doves and eagles; or reptiles, as snakes, lizards,
and frogs. (Fig. 53.) Their spots and colors give sometimes the
appearance of leopard or tiger skins. These resemblances are indicated
in their generic and specific names. Some parts of the petals of these
flowers display peculiar irritability, for the purpose of scattering the
fertilizing pollen. As the visits of insects are often subsidiary to the
fertilization of Orchids, they have attracted much attention from
naturalists. They abound chiefly in moist tropical climates.
[Illustration: FIG. 54.—The White Lily, (_Lilium album_.) ]
9. The LILY family (_Liliaceæ_) includes many showy garden flowers, as
Tulips, Lilies, Dogtooth-violets, and Tuberoses. (Fig. 54.) It is
divided into several tribes, as the Onion, or Squill tribe, the Asphodel
tribe, the Lily-of-the-valley tribe, the Aloes tribe, and the Asparagus
tribe. In the latter tribe are placed the Dragon-trees, the most
gigantic of the order. There is one in the Island of Teneriffe which is
described as seventy feet high and forty-six feet in circumference at
the base. The flowers are small. From some species of Dragon-tree the
Sandwich Islanders prepare an intoxicating liquor called _ava_.
The inspissated juice of several species of Aloe is used in medicine as
a cathartic, and the bulb of the Squill is imported from the coasts of
the Mediterranean, and is valued for its diuretic, expectorant, and
other properties.
A species of Onion called Camass is used by the Indians of Oregon as
food.
Textile fibers are procured from New Zealand flax (_Phormium_) and from
the _Yucca_, or Adam’s needle.
10. The SCREW-PINE family (_Pandanus_) contains several species which
exhibit a semblance of instinct in the development of aerial roots at
different distances on the stem, by which their life is prolonged. Their
leaves are arranged in a spiral, hence the name, Screw-pine.
[Illustration: FIG. 55.—Bulrush. ]
11. The ARUM family contains the Cuckoo-pint tribe, the Bulrush tribe,
(Fig. 55,) the Sweet-flag tribe, and the Duckweed tribe. In the Duckweed
(_Lemna_) we see at a casual glance nothing but a green scale floating
on the water, which is in reality a compound of both root and stem. A
careful observation in summer may lead to the discovery of minute
straw-colored anthers on the edges of the plants, and near these a
narrow slit, which, on being enlarged, will show the simple flower, like
a membraneous bag, and containing two stamens and one ovary, with its
style and simple stigma.
11. Protophytes, Thallogens, and Acrogens have been classed together in
the artificial system of Linnæus as _Cryptogamia_, (from _cryptus_,
hidden, and _gamos_, nuptials,) in allusion to the inconspicuous
character of their reproductive organs; while Endogens and Exogens are
called _Phanerogamia_, (_phaneros_, visible, and _gamos_, nuptials,)
since they have perceptible reproductive organs formed of _stamens_ and
_pistils_. To these essential parts we frequently find two envelopes
added, the _calyx_ and _corolla_. These parts make up the flower, and
the Phanerogamia are not infrequently known as flowering plants.
The flower consists of whorled leaves placed on an axis, the internodes
of which are not developed. There are usually four of these whorls. The
outer whorl is the calyx, the next the corolla, the third the stamens,
and the innermost the pistil. In Exogens the calyx is usually green and
the corolla colored, but in Endogens both frequently display rich
coloring, and are apt to be confounded, so that the term _perianth_ is
usually applied to the flowers of Endogens, whether colored or
otherwise, (_peri_, around; _anthos_, flower.)
[Illustration: FIG. 56.—A. Sectional view of the flower, showing the
vertical disposition of the whorls. _a._ Sepal of calyx. _b._ Petal of
corolla. _c._ Filament of stamen. _d._ Anther of stamen. _e._ Ovary of
pistil. _f._ Style of pistil. _g._ Stigma of pistil. B. Plan of the
typical flower of an exogenous plant, showing the horizontal disposition
of its parts. _a._ Sepal. _b._ Petal. _c._ _c._ Stamens in two distinct
whorls. _d._ Carpel or ovary, inclosing an ovule, attached by its
funiculus. C. Various parts of the clove. _a._ Flower of the clove or
pink. _b._ Vertical and middle section of the flower. _c._ Flower
reduced to its male and female portions; the stamens are six in
number—four large, (in pairs,) and two small. _d._ One of the petals.
_e._ Horizontal section of the ovary, or seed-vessel; showing the
insertion of the ovules. _f._ Fruit at the moment of expansion. _g._
Seed, with its funiculus. _h._ Vertical section of the seed and its
embryonic contents. _i._ The embryo alone. _k._ Horizontal section of
the seed and its embryonic contents. ]
The parts of the calyx, when separate, are called _sepals_, and the
leaves of the corolla _petals_. Stamens have two parts, the _filament_,
or stalk, and the _anther_, or broader portion, corresponding to the
folded blade of the leaf, and containing fertilizing grains called
_pollen_. The pistil is also made up of two parts, the _ovary_,
containing ovules or young seeds, and the _stigma_, a cellular secreting
body for the reception of the pollen-grains. This is sometimes sessile,
or resting on the ovary, and sometimes elevated on a stalk, or _style_.
Like the other whorls, the pistil is made up of one or more modified
leaves, named _carpels_. (Fig. 56.)
Some flowers have no stamens, and are called female flowers; others have
no pistil, and are male flowers; but both stamens and pistils are always
present, either on the same plant or on different plants. Some flowers
have neither calyx, corolla, nor stamens; others, neither calyx,
corolla, nor pistil. If they have no corolla they are _incomplete_, and
if corolla and calyx are both absent they are _naked_.
The general axis of inflorescence is called _rachis_; the stalk
supporting a flower or a cluster of flowers is a _peduncle_, and, if
small branches are given off by it, they are called _pedicels_.
Sometimes the floral axis is shortened, and is flat, convex, or concave,
bearing numerous flowers, as in the Daisy. It is then called a
_receptacle_.
Flowers are always the termination of an axis, branch, or bough, and the
order governing their arrangement is a repetition of that which governs
the ramification of the plant.
_Bracts_, or floral leaves, are leaves from which the floral axis, or
the individual flowers, arise. Sometimes they are colored and may be
mistaken for parts of the corolla, and at other times they are
undeveloped. Bracts are generally deciduous, but occasionally persist,
and even form part of the fruit, as in the cones of Firs and the fruit
of the Pine-apple. In catkins (or imperfect unisexual sessile flowers on
a spike, as in the Willow or Hazel) the bracts are called _scales_. A
whorl of bracts is an _involucre_. These are sometimes adherent, as in
the cup of the Acorn. A sheathing bract inclosing one or more flowers is
a _spathe_. This is common among Endogens, as in Calla, Arum, and the
Palms. In Grasses the outer scales are considered as sterile bracts, and
have received the name of _glumes_.
The various modes of inflorescence is a subject of profound study with
botanists, but its details are too extensive for the design of the
present work. As stated in Chap. IV, Sec. 11, the parts of the flower,
as regards their development, structure, and arrangement, may all be
referred to the leaf as a type. They begin like leaves in cellular
projections, in which fibro-vascular tissue is ultimately formed; they
are arranged in a more or less spiral manner, and they are often
partially or entirely changed into leaves. These facts confirm Goethe’s
doctrine that all the parts of the flower are altered leaves.
12. In the type of Endogens we meet with a great variety of flowers,
some perfectly organized, as the Lily, and others, as the Duckweed and
Bulrushes, quite incomplete. Yet even in the more lowly forms we meet
with abundant examples of the care of a beneficent Providence
accomplishing intelligent designs by various ways, but all indicative of
Divine wisdom. In the Branched Bur-reed (_Sparganium ramosum_) the
branches bear yellow balls of staminate, or barren flowers, and green
pistillate, or fertile florets. “What happens in this case,” says Dr.
Lindley, “occurs also in all instances in which the stamens are
separated from the pistils in different flowers on the same plant; we
invariably find that the stamens are placed on the uppermost parts of
the branch above the pistils, an arrangement which is no doubt provided
to facilitate the scattering of their pollen upon the stigmas. If they
were placed below the pistils it would be much more difficult for the
pollen to reach the stigma, and consequently, the great end of the
creation of the stamens would be almost frustrated. We find, however,
that every thing is foreseen and provided for by Providence, with the
same care in these little plants as in the most exalted and perfect of
the works of nature; and that even so apparently useless and
insignificant a weed as the Bur-reed contains the most convincing
evidence of the worthlessness of the opinions of those who, denying the
existence of the Deity, would have the world believe that living things
are the mere result of a fortuitous concourse of atoms, attracting and
repelling each other with different degrees of force.”[21] The recent
elaborate observations of Darwin, Sir J. Lubbock, and others, upon the
fertilization of plants, as the Orchids, by the visits of insects,
although sought to be explained by the principle of “unconscious natural
selection,” finds a more ready and satisfactory explanation in the case
of an ever-present Providence, since if the colors, and honey, and
structure of the flowers are “all arranged with reference to the visits
of insects,”[22] the structure and habits of insects are equally adapted
to the fertilization of the flowers. From the design we infer a
Designer.
CHAPTER X.
E X O G E N S .
In all places, then, and in all seasons,
Flowers expand their light and soul-like wings,
Teaching us, by most persuasive reasons,
How akin they are to human things.
And with childlike, credulous affection,
We behold their tender buds expand,
Emblems of our own great resurrection,
Emblems of the bright and better land.
—LONGFELLOW.
1. The term Exogen (from _exo_, outward, and _gennao_, to produce) is
applied to those plants which produce woody and vascular layers toward
the circumference. It is the largest class, or type, in the vegetable
kingdom, including about 7,000 genera and 70,000 species of flowering
plants.
External to the woody layers, and between them and the bark, is a layer
of semifluid mucilaginous matter called _Cambium_. Its cells are
exceedingly delicate. New cells are continually being added, on the
inner side of the Cambium layer, to the thickness of the wood, and on
the outer side of it, to the thickness of the bark, increasing the
diameter of the axis of the plant.
[Illustration: FIG. 57.—A. Mode of growth in stem. B. In root. A. _a._
Growing cells in stem, which multiply by fission. _b._ Cambium,
elaborated by growing cells. B. _a._ Growing cells in root. _b._ Cells
produced by growing cells. _c._ Cap, (pileorhiza.) C. Root of duckweed,
(magnified.) _a._ Growing point. _b._ Root-sheath. _c._ Cap. _d._ Root.
]
At the apex of the stem, and at that of the root, the Cambium layer is
continuous with the cells which retain the power of dividing in these
localities.
The general appearance of the axis of an exogenous plant is that of a
double cone; one cone representing the stem, the other the root; the
growing part of both being bathed in the cambium fluid.
In the growing stem the terminal cells (_a._ Fig. 57, A) multiply and
enlarge, while they furnish new cells to the cambium layer. In the root,
however, the multiplying cells are not quite at the extremity. A sort of
cap is formed by the growing cells, (_pileorhiza_,) and receives
additions to its interior, which push out the layers external to them.
(Fig. 57, B, C.) Thus efficient protection is afforded to the
newly-formed tissue.
[Illustration: FIG. 58.—Diagrammatic Section of a Flowering Plant,
showing the different tissues. A. Ascending axis. B. Descending axis.
_s._ Surface of soil. _c._ _c._ Appendages. _d._ Growing point of stem.
_e._ Epidermis. _f._ _f._ Stomata. _g._ Layer containing chlorophyll,
(marked by the dotted lines.) _k._ _k._ Woody fiber. _l._ _m._ _n._
Pith, spiral vessel, and dotted duct—all air passages. _r._ _r._ Roots.
_t._ Growing point of roots. _w._ Cap, (pileorhiza.) ]
The general arrangement of the tissues of a flowering plant may be seen
in Fig. 58. Air passages are both intercellular and vascular, the latter
in Exogens being dotted ducts and spiral vessels. The bark contains
elongated _liber_ or bast cells, but there are no scalariform vessels as
in Acrogens. The chlorophyll (Chap. VI, Sec. 2) is found chiefly in the
cells immediately under the epidermis. See also Figs. 15 and 16. The
roots are supplied with water containing carbonic acid, air, and oxygen,
in addition to the minerals and decomposing organic matter (or _humus_)
contained in the soil. Some plants grow without attachment to the soil,
deriving all their nutriment from the air, and are called _Epiphytes_,
(_epi_, upon; _phyton_, a plant,) from being generally found on trees.
They differ from true parasites, since the latter prolong their tissues
into other plants, and prey upon them. The Orchids may illustrate the
first, and the Dodder and Mistletoe the latter kind.
The only structure capable of effecting the chemical changes necessary
to plant nutrition is the chlorophyll, which is most abundant in the
leaves; hence, the materials which supply food must be carried up to the
leaves. The ascent of fluid from the root to the leaves takes place by
means of two distinct forces—a pushing force, caused by absorption by
the extremities of the rootlets, and endosmose (Chap. IV, Sec. 3) from
cell to cell; and a pulling force, produced by evaporation from the
surface of the leaves.
The appendages of the root are the rootlets, and of the stem, the
leaves. Leaves are developed from the nodes, and the internodes (Chap.
VIII, Sec. 2:) become shorter toward the summit of the stem, which ends
in a terminal _bud_. Buds are also developed in the axils of the leaves,
and some of them grow into branches, which repeat the characters of the
stem; but others, when the plant is fully developed, grow into stalks
which support the flowers.
In Chap. IX, Sec. 11, will be found a general description of the flower,
and in Chap. IV, Sec. 11, an account of the tissues forming the leaf.
The arrangement of leaves and branches is also a subject of biological
interest. The mode in which branches come off from the nodes gives rise
to various forms of trees, such as pyramidal, spreading, or weeping. In
the Italian Poplar and Cypress the branches are erect, forming acute
angles with the upper part of the stem; in the Oak and Cedar they are
spreading; while in the Weeping Willow and Birch they are pendulous from
their flexibility. Leaves also are placed in a fixed order for every
species of plant, and this order may be expressed by an arithmetical
formula. The arrangement of the leaves on the axis is called
_phyllotaxis_, (_phyllon_, a leaf; _taxis_, order.) Each node of the
axis may give rise to a leaf, but sometimes several nodes are
approximated nearly together, and then several leaves may be produced at
the same height on the stem. When two leaves are at the same level, one
on each side of the stem, they are called _opposite_; when a circle of
leaves is thus produced it is called a _verticil_, or _whorl_. When a
single leaf is produced at a node, and the nodes are separated, the
leaves are _alternate_. The relative position of alternate leaves varies
in different plants, but is tolerably uniform in each species. In a
regularly-formed branch covered with leaves, if a thread is passed from
one to the other, turning always in the same direction, a spiral is
described, and a certain number of leaves and of complete turns occur
before reaching the leaf directly above that which began the series.
This may be expressed by a fraction, the numerator of which indicates
the number of turns, and the denominator the number of leaves in the
spiral cycle. In the Peach and Plum-tree the cycle embraces five leaves,
and the spiral goes twice around the branch. This is expressed by the
formula ⅖. In the Alder three leaves constitute the cycle, and the
spiral has only a single turn on the stem; the disposition of its leaves
is represented by the fraction ⅓.
In Exogenous plants the leaves are reticulated, and usually articulated
to the stem. The flowers are formed upon a quinary or quaternary type;
that is, their parts are in sets of fives or fours, instead of sets of
threes, as Endogens. The embryo has two opposite cotyledons, or
seed-lobes, which gives the term Dicotyledonous to the type.
2. According to the natural system of De Candolle, which is usually
followed, Exogens are subdivided as follows:
1.) THALAMIFLORÆ, (_Thalamus_, receptacle, and _flos_, flower.) Calyx
and corolla present; petals distinct, inserted into the receptacle;
stamens hypogynous, or growing from below the ovary, as Ranunculus,
Magnolia, Poppy, Violet, Geranium, etc.
2.) CALYCIFLORA. A calyx and corolla present, the petals distinct, but
the stamens are perigynous, or attached to the calyx; as Rhamnus, the
Leguminose family, the Rose family, the Syringa, the Passion-flower,
Cactus, etc.
3.) COROLLIFLORÆ. Calyx and corolla present; petals united, bearing the
stamens; as the Honeysuckle, Madder, Teazel, Composite family, Heaths,
etc.
4.) MONOCHLAMYDEÆ, (_Monos_, one; _chlamus_, a cloak, or covering.)
Sometimes called INCOMPLETÆ. Corolla wanting; a calyx or simple perianth
present. (Even this sometimes absent.) It is divided into two sections:
A. _Angiospermæ._ Seeds contained in an ovary, as Amaranth, Phytolacca,
Buckwheat, Laurel, Begonia, Nettle, Fig, and the Catkin-bearing family.
B. _Gymnospermæ._ Seeds naked. Their woody tissue is marked by disks,
(Chap. IV. Sec. 9;) as the Coniferæ and Cycas family.
[Illustration: FIG. 59.—Pines, (_Pinus Sylvestris_.) ]
3. Among the INCOMPLETE Exogens, belonging to the section of
_Gymnosperms_, or naked-seeded Exogens, are found the Cycas family,
(CYCADACEÆ,) which greatly resemble the Palms and Tree-ferns, and the
Cone-bearing family, (CONIFERÆ,) divided into the Fir and Spruce tribe,
(_Abietineæ_,) the Cypress tribe, (_Cupressineæ_,) the Yew tribe,
(_Taxineæ_,) and the Joint-fir tribe, (_Gnetaceæ_.)
The Coniferous plants are noble trees or evergreen shrubs, and furnish
valuable timber and other important products, as turpentine, pitch, and
resin. The Pine (Fig. 59) is one of the most perfect trees of the
forest, considered in respect to its beauty and uses. “Its character and
glory,” writes Mr. Ruskin, “consist in its right doing of its hard duty,
and forward climbing into those spots of forlorn hope where it alone can
bear witness of the kindness of the Spirit that cutteth out rivers among
the rocks, as it covers the valleys with corn; and there, in its vanward
place, and only there, where nothing is withdrawn for it, nor hurt by
it, and where nothing can take part of its honor, nor usurp its throne,
are its strength, and fairness, and price, and goodness in the sight of
God to be truly estimated.”
4. Among the ANGIOSPERM EXOGENS, or those of the Incomplete class whose
seeds are inclosed in an ovary. The principal families are the Marvel of
Peru, the Amaranth, the Phytolacca, the Buckwheat, the Begonia, the
Laurel, the Nutmeg, the Oleaster, the Daphne, the Sandalwood, the
Birthwort, the Pitcher-plant, the Rhizogen, the Spurge, the Nettle, the
Pepper, the Walnut, and the Catkin-bearing families.
To the Buckwheat family (POLYGONACEÆ) belong the Buckwheat, (_Fagopyrum
esculentum_,) the Sorrel, (_Rumex Acetosa_,) and Rhubarb, (_Rheum
palmatum_.) In the Laurel family are the Laurel, Bay, Camphor,
Sassafras, and Cinnamon trees.
[Illustration: FIG. 60.—Pitcher-plant,
(_Nepenthes distillatoria_.) ]
The Pitcher-plants (_Nepenthes_) are among the curiosities of the
vegetable world, on account of the pitcher formed at the end of the
leaf. This is furnished with a lid, and contains a limpid fluid secreted
by glands in the cavity, and in sufficient quantity to drown flies and
other insects which fall into it. (Fig. 60.) Since the publication of
Mr. Darwin’s “Insectivorous Plants” these secreting leaves (together
with those of several other species) have attracted much attention, as
in all probability there is in these arrangements provision for a true
digestion, as in the case of animals.
The _Euphorbiaceæ_, or Spurge family, contains many trees, shrubs, and
herbs, abounding in acrid milky juice, which is generally poisonous.
_Siphonia elastica_ is one of the plants which supplies caoutchouc, or
India-rubber. The seeds of _Croton Tiglium_ affords Croton oil, and
those of _Ricinus communis_ (or _Palma Christi_) furnish Castor-oil. In
the root of _Janipha Manihot_ there is much starchy matter mingled with
a volatile poison. The latter is removed by heat or washing, and the
starch is used as Cassava bread. Tapioca and Brazilian Arrowroot are
said to be procured in this way.
In the NETTLE family are about six hundred species, including the common
Nettle, Hemp, Hop, Elm, Fig, Mulberry, Bread-fruit, the Banyan, (_Ficus
indica_,) etc.
[Illustration: FIG. 61.—Woodland Scenery. ]
The Catkin-bearing family (AMENTACEÆ) is the largest and most important
of this order, since it contains all the most important timber trees.
(Fig. 61.) The Alder, Birch, Willow, Poplar, Oak, Chestnut, Hornbeam,
and Plane are here brought together because of the similarity of their
fructification. They produce flowers of one sex only, the males of which
are in catkins, in which the flowers have, neither calyx nor corolla,
but merely a single scale. Their bark has an astringent quality from the
presence of tannin, and some, as the Willow, yield a valuable tonic
febrifuge, (_Salicin_.) The fruit of many species contains starchy
matter, rendering it edible by man or animals, as the acorns of oak,
mast of birch, nuts of the hazel, etc.
5. In the order COROLLIFLORÆ, or Exogens having the petals united, and
bearing the stamens, are to be found the Mistletoe, the Honeysuckle,
Peruvian bark, Valerian, Teazel, Harebell, Lobelia, Heath, Cranberry,
Ebony, Holly, Jasmine, Olive, Asclepias, Dog-bane, Gentian,
Trumpet-flower, Phlox, Convolvulus, Borage, Nightshade, Figwort,
Labiate, Vervain, Acanthus, Primrose, and Composite families.
The Honeysuckle family (CAPRIFOLIACEÆ) is divided into the true
Honeysuckle tribe (_Lonicereæ_) and the Elder tribe, (_Sambuceæ_.)
The Peruvian Bark family (RUBIACEÆ) contains, in addition to the
Peruvian bark of commerce, (_Cinchona_,) the Ipecacuanha, (_Cephaelis
Ipecacuanha_,) the Coffee-tree, (_Coffea arabica_,) and the Madder,
(_Rubia tinctoria_.)
The Heaths (ERICACEÆ) contain many beautiful and showy plants, as the
Rhododendrons, Azaleas, and Kalmias. The Partridge-berry, (_Gaultheria
procumbeus_,) the Bear-berry, (_Arctostaphylos Uva-Ursi_,) and the
Chimaphilla, (_Pyrola umbellata_,) are sometimes used in medicine.
In the Olive family (OLEACEÆ) is placed the Olive, Lilac or Syringa, and
the Ash, (_Fraxinus excelsior_.)
The Gentians (GENTIANACEÆ) are mostly dwarf herbaceous plants, with deep
blue flowers.
The CONVOLVULACEÆ, or Bind-weed family, are twining plants with showy
flowers, except the tribe of Dodders, (_Cuscuteæ_,) which are leafless
parasites. Here we find the Jalap, and Scammony, and Sweet-Potato,
(_Batatas edulis_.)
The Nightshade family (SOLANACEÆ) contains the Potato, (_Solanum
tuberosum_,) the Deadly Nightshade, (_Atropa Belladonna_,) the Henbane,
(_Hyoscyamus niger_,) the Thorn-apple, (_Datura Stramonium_,) Tobacco,
(_Nicotiana Tabacum_,) Cayenne-pepper, (_Capsicum annium_,) the Tomato,
(_Lycopersicum esculentum_,) etc.
The LABIATÆ are characterized by two long and two short stamens, four
little nuts or naked seeds, and irregular corollas. The plants are
generally fragrant and aromatic, and none of them are injurious. Many
are used in medicine as carminatives. Mint, Lavender, Sage, Savory, and
Balm, are examples of the family. From Thyme a sort of camphor has been
procured called Thymol, which has similar antiseptic properties to
Carbolic acid, but with pleasant odor.
The family COMPOSITÆ is a very extensive one. The florets are arranged
in involucrated heads, and the anthers cohere into a cylinder. It is
subdivided into three sections: 1. _Cynarocephalæ_, (from _cynara_, the
Artichoke,) having all the flowers tubular; the involucre, hard,
conical, and often spiny, as the Thistle, Burdock, etc. 2.
_Corymbiferæ_, (_corymbus_, a comb, and _fero_, to bear,) having tubular
florets in the disk (center) and ligulate in circumference, (or ray;)
involucre hemispherical, leafy, or scaly, rarely spiny, as Feverfew,
Wormwood, Tansy, Arnica, and Sunflower. 3. _Cichoraceæ_, (_cichorium_,
succory,) having the florets all ligulate, as Chicory, Dandelion, and
Lettuce. The Daisies, Asters, Chrysanthemums, and Dahlias of the gardens
are all composite flowers.
6. In the subdivision of CALYCIFLOREÆ are placed Exogens which have a
calyx, and corolla with distinct petals, and whose stamens are attached
to the calyx.
In the Buckthorn family (RHAMNACEÆ) we find the genus Rhamnus, several
of whose species yield cathartic medicine, and Ceanothus, or Mountain
tea.
The Cashew-nut family (ANACARDIACEÆ) contains the Cashew-nut, (_Pistacia
vera_,) _Rhus Toxicodendron_, or Poison-oak, and many plants which
furnish varnishes, as the Japan lacquer, (_Stagmaria verniciflua_.)
A number of fragrant balsamic resins, including myrrh, (_Balsamodendron
Myrrha_,) are obtained from plants of the Amyris family, (AMYRIDACEÆ.)
The Pea and Bean family (LEGUMINOSÆ) is very extensive, containing more
than four hundred and fifty genera and six thousand five hundred
species. It embraces many valuable medicinal plants, as those yielding
Senna, Gum-arabic, Tragacanth, Catechu, and Kino; important dyes, as
Indigo and Logwood; valuable timber-trees, as Locust-tree and Rosewood;
and plants furnishing nutritious food, as the Bean and Pea. This order
has been divided into three sub-orders, 1. _Papilionaceæ_; having
papilionaceous flowers, the petals imbricated in æstivation, and the
upper one exterior. The plants of this section often have beautiful
showy flowers, as Robinia, Laburnum, Lupinus, etc. The various kinds of
Clover, Beans, Peas, and Pulse belong to it. The _Glycyrrhiza glabra_,
or plant yielding liquorice-root, the _Myroxylon peruiferum_, or source
of the Balsam of Peru, and many other plants having medicinal qualities,
are found here. 2. _Cæsalpineæ._ Flowers irregular, but not
papilionaceous, petals spreading, imbricated in æstivation, upper one
interior. Here we find the place of several plants used in medicine, as
various species of _Cassia_ or Senna, the Tamarind-tree, and the
Logwood, (_Hæmatoxylon_.) 3. _Mimoseæ._ Flowers regular, petals valvate
(without overlapping) in æstivation; as the different species of
_Acacia_, yielding Gum Arabic, and the _Mimosæ_, or Sensitive plants.
The Rose family (ROSACEÆ) is also a very large one belonging to the
_Calycifloreæ_. Its sub-orders are, 1.) _Chrysobalaneæ_, petals and
stamens irregular, ovary stipitate, its stalk adhering to the side of
the calyx, style basilar, fruit a 1-2-celled drupe, (or fleshy fruit.)
2.) _Amygdaleæ_, tube of calyx lined with a disk, styles terminal, fruit
a drupe. 3.) _Spiræeæ_, calyx-tube herbaceous, lined with a disk, fruit
of numerous follicles, seeds apterous. 4.) _Quillaieæ_, flowers
unisexual, calyx-tube herbaceous, fruit capsular, seeds winged at the
apex. 5.) _Sanguisorbeæ_, petals none, tube of calyx thickened and
indurated, stamens definite, nut solitary, inclosed in the calycine
tube. 6.) _Potentilleæ_, calyx-tube herbaceous, lined with a disk which
sometimes becomes fleshy, fruit consisting of numerous achænia, (small,
brittle, seed-like fruit.) 7.) _Roseæ_, calyx-tube contracted at the
mouth, becoming fleshy, lined with a disk, and covering numerous hairy
achænia. 8.) _Pomeæ_, tube of calyx more or less globose, ovary fleshy
and juicy, lined with a thin disk, fruit a 1-5-celled, or spuriously
10-celled, pomum. Many of the plants of this order yield edible fruits,
as Raspberries, Strawberries, Plums, Apples, Pears, Cherries, Peaches,
and Apricots. Plants of the sub-order Amygdaleæ are remarkable for the
presence of hydrocyanic acid, as in the kernel of the Almond,
(_Amygdalus communis_,) especially the bitter Almond; the leaves of the
Peach, (_Amygdalus persica_,) and of the Cherry-laurel, (_Prunus
Laurocerasus_.) The sub-order Pomeæ supplies Apples, Pears, and Quinces.
The seeds contain hydrocyanic acid. The other sub-orders have plants
distinguished by astringent and tonic properties, as the root of
_Potentilla Tormentilla_, and the petals of _Rosa gallica_, the Red
Rose.
[Illustration: FIG. 62.—A Mangrove Forest. ]
The RHIZOPHORACEÆ, or Mangrove family, is named after _Rhizophora
Mangle_, the Mangrove, which forms thickets at the muddy mouths of
rivers in tropical countries, and sends out adventitious roots which
often raise up the main trunk, and give the tree the appearance of being
supported on stalks. (Fig. 62.) The fruit is sweet and edible.
The Myrtle family (MYRTACEÆ) contains trees or shrubs which are usually
natives of warm countries. Some of the genera are peculiar to Australia,
as the Eucalyptus, or Blue Gum-tree, which is being planted extensively
in California. It is a rapid grower, and promises to be serviceable as a
forest tree. It contains a medicinal balsamic resin. The Pimento,
(_Myrtus Pimenta_,) the Pomegranate, (_Punica Granatum_,) and various
species of edible Guavas and Rose-apples belong to this order.
The Evening Primrose (_Œnothera_) and the _Fuchsia_ belong to the order
ONAGRACEÆ, or the Evening Primrose family.
The Cucumber family (CUCURBITACEÆ) contains many plants that are drastic
purgatives, and others whose fruits under cultivation are edible, as the
Melon and the Colocynth, both species of the same genus, (_Cucumis_.)
The Passion-flowers (PASSIFLORACEÆ) received their name from a fancied
resemblance to the scenes at Calvary. The superstitious monks saw in the
five anthers a resemblance to the wounds of Christ; in the triple style,
the three nails on the cross; in the central pillar, the cross itself;
and in the filamentous processes, the rays of light round the Saviour,
or the crown of thorns.
The PORTULACACEÆ, or Purslane family, are chiefly herbaceous plants,
found in dry, barren situations, or on the sea-shore. Some of them have
tuberous roots which have been proposed as substitutes for the potato,
as _Claytonia tuberosa_, and _Melloca tuberosa_. The first is a Siberian
plant, the other a native of Peru.
[Illustration: FIG. 63.—A Group of Cactaceæ. ]
The Cactus family (CACTACEÆ) contains many succulent plants, destitute,
for the most part, of leaves, the place of which is supplied by fleshy
stems of grotesque figures. Some are angular, and grow to a height of
thirty feet; others are roundish, covered with stiff spines, and not
over a few inches high. Their flowers are often large and beautiful,
varying from pure white to rich scarlet, or purple. Some are
night-flowering, as the _Cereus grandiflorus_. In Mexico and Southern
California there are a large number of species, some of which are of
gigantic size. (Fig. 63.)
The Gooseberry and Currant family, (GROSSULARIACEÆ,) the Saxifrage
family, (SAXIFRAGACEÆ,) the Witch-hazel family, (HAMAMELIDACEÆ,) are all
of this section of Exogens, with many others. The Umbelliferous family
(UMBELLIFEREÆ) are characterized by the radiating or umbrella-like
arrangement of the florets. The properties of the plants of this family
are various. Some yield articles of diet, as the Parsnip, (_Pastinaca
sativa_,) Carrot, (_Daucus Carota_,) and Parsley, (_Petroselinum
sativum_.) Others yield milky juices, which dry into a fetid gum-resin,
as the _Ferula Assafœtida_, yielding Assafœtida, and _Dorema
Ammoniacum_, which produces Ammoniae. Others again supply a carminative
and aromatic oil, as Caraway-seeds (_Carum Carui_) and Fennel,
(_Fæniculum dulce_.) Some species are quite poisonous, as the _Conium
maculatum_, or Hemlock, which contains a volatile alkaline poison,
called Conia.
7. In the sub-class, or order THALAMIFLORÆ, the stamens are inserted
under the pistil into the thalamus, or receptacle. The petals, also, are
inserted into the receptacle. In some cases the petals are abortive, and
it becomes hard to determine whether the plant belongs to this division
or to Monochlamydeæ.
The RANUNCULACEÆ, or Crowfoot family, is characterized chiefly by having
several distinct carpels, above numerous stamens. The plants are
generally narcotic acid poisons. The Ranunculus, Anemone, Larkspur,
Aconite, and Peony are examples.
The leaves of _Aconitum Napellus_, or Monkshood, are used in medicine,
as well as the rhizome of _Podophyllum peltatum_, or May Apple.
[Illustration: FIG. 64.—The Opium-Plant,
(_Papaver somniferum_.) ]
The Poppy family (PAPAVERACEÆ) differs from the last in having the
carpels united into an undivided ovary, and in having milky or colored
juice. Opium is the dried juice of _Papaver somniferum_, (Fig. 64,) or
Poppy, and its varieties. The Celandine (_Chelidonium majus_) yields an
orange-colored juice, which is said to be acrid. In the leaf of this
plant may be seen under the microscope the movement of the sap in the
laticiferous vessels. _Sanguinaria canadensis_, or Blood-root, has
emetic and cathartic properties. The yellow California Poppy
(_Eschscholtzia_) is remarkable for the two sepals of its calyx adhering
at the edge, and separating at the base by the growth of the flower, so
as to form a sort of calyptra, or hood, over the unexpanded petals,
resembling the extinguisher of a candle.
MAGNOLIACEÆ, the Magnolia family, contains the well-known Magnolias,
remarkable for large odoriferous flowers, the Swamp Sassafras, (_M.
glauca_,) whose bark is used as a substitute for the Peruvian bark, and
the _Liriodendron tulipifera_, or Tulip-tree, etc.
The Side-saddle family (SARRACENIACEÆ) contains the genera _Sarracenia_
and _Darlingtonia_, which (like Nepenthes) are characterized by a
pitcher-like appendage to the leaf, containing a fluid secretion,
supposed to have the power of digesting insects which fall into it.
CRUCIFERÆ, the Cruciferous, or Cress-wort family, known so readily by
their four cruciate petals, contains a large number of plants, none of
which are poisonous, although some are stimulant and even acrid. Most of
the common culinary vegetables belong to this order, as Cabbage,
Cauliflower, Turnip, Radish, Cress, and Mustard. Many garden flowers
also are of this family, as Wallflower and Alyssum.
The Violet family, (VIOLACEÆ,) the Mignonette family, (RESEDACEÆ,) the
Berberry family, (BERBERIDACEÆ,) the Rock-Rose family, (CISTACEÆ,) the
St. John’s-wort family, (HYPERICACEÆ,) the Vine family, (VITACEÆ,) the
Geranium, or Crane’s-bill family, (GERANIACEÆ,) the Wood-sorrel family,
(OXALIDACEÆ,) and many others, must be passed by, since space forbids us
to enlarge.
The Quassia family (SIMARUBACEÆ) is noted for the bitter and tonic
principle contained in the wood of _Quassia amara_, and other species.
The Rue family (RUTACEÆ) is also known in medicine, since it furnishes
Rue, Buchu, (_Barosma crenata_,) and other agents.
The Flax family (LINACEÆ) furnishes the well-known Flax, (_Linum
usitatissimum_,) whose inner bark yields linen and cambric. The seeds
are mucilaginous and oleaginous.
[Illustration: FIG. 65.—Common water Lily, (_Nymphæa alba_.) ]
The Water-lily family (NYMPHÆCEÆ) contains plants with showy flowers.
(Fig. 65.) _Victoria regina_ is one of the largest known, the white and
rosy flowers being four feet in diameter, and the leaves fifteen feet
across, according to Schlieden.
DROSERACEÆ, the Sundew family, is remarkable for its insectivorous
properties. The _Droseras_ are furnished with glandular hairs, which
exhibit drops of fluid in sunshine, hence the name.
_Dionæa muscipula_, Venus’s Fly-trap, has the laminæ of the leaves in
two halves, each furnished with three irritable hairs, which, on being
touched, cause the folding of the divisions in an upward direction.
The Chickweed and Pink family (CARYOPHYLLACEÆ) contains all the
Carnations, or Pinks, (_Dianthus_,) Chickweed, (_Stellaria media_,) etc.
[Illustration: FIG. 66.The Cotton-plant, (_Gossypium_.) ]
The Mallow family (MALVACEÆ) contains many wholesome mucilaginous
plants. The Mallow, (_Malva_,) the Hollyhock, (_Althæa rosea_,) the
Abutilon, (_A. esculentum_,) and the Cotton-plant, (_Gossypium_,) belong
here. (Fig. 66.) The produce of the latter plant employs the labor of a
million and a half of people in England alone, and furnishes clothing to
hundreds of millions.
The Tea family (TERNSTRÆMIACEÆ) has in it the beautiful Camellias of
Japan, and the plants which furnish tea, (_Theaviridis_ and _Bohea_.)
The use of the leaves of these plants is immense, no less than fifty-six
millions of pounds being imported into Great Britain in a single year,
(1846.) The bitter principle in tea, called _theine_, may be procured by
adding a slight excess of acetate of lead to a decoction of tea,
filtering hot, evaporating, and subliming.
The Orange family (AURANTIACEÆ) contains about a hundred species. The
plants contain receptacles of volatile oil. The fruit has an acid or
subacid pulp, and the wood is compact. The Orange, Lemon, Lime, Citron,
and Shaddock belong here.
ACERACEÆ, the Maple family, contains the Maple and Sycamore, (_Acer
pseudo-platanus_.) The Sugar Maple (_A. saccharinum_) yields a sap from
which sugar is manufactured.
The Mahogany family (CEDREIACEÆ) contains plants with an aromatic
fragrance. _Swietenia Mahogoni_ supplies the well-known mahogany wood,
and _Chloroxylon Swietenia_, satin wood.
8. In the rapid sketch we have made of the vegetable kingdom, we have
omitted the minute botanical details characteristic of each family, and
have only given the principal differences and resemblances of types and
classes, with some few representative forms in the most important
families. These general peculiarities of plants serve in a great degree
to define the character of landscape scenery in various parts of the
world. Gray and withered Lichens clothe the barren confines of
vegetation toward the snow-line of mountains or at the north, while
Mosses form a silken cushion over rock and soil with their delicate
leaflets.
Grasses are characterized by their sociability, and call forth agreeable
sensations by their soft carpet of green and pliant leaves. The Sedges,
on the contrary, with stiff and rugged stems and leaves, rejected by
cattle, awaken no pleasing associations. In tropical climates, as in
Hindustan, the tall Bamboo sometimes overtops the trees, and forms a
meadow above the forest. There the Plantain stem swells with sap, the
leaves expand and are split by the wind, and the great flower-bunches
beam with intense color. Between the reeds and the banana plants the
lilies may be placed. The arrow-shaped leaves of the Aroids, with
strange and often brightly-colored spathes, mark the transition to the
Orchids.
The stems as well as the leaves of plants often give character to a
landscape, as in the Heaths—low, branching, dull-green or gray shrubs,
whose blossoms scarcely obliterate the melancholy impression produced
where they abound. The arborescent Heaths (_Casuarinæ_) form many of the
gloomy woods of Australia. Still more striking are the forms of the
thorny Cactuses, (Fig. 63,) consisting merely of fleshy stems and
branches of singular shapes. The Yuccas of Mexico, the great African
Aloes, and the Grass-trees of Australia, with their solid liliaceous
leaves, of a dull green, afford a picture of immovable repose. The
stiff, shining leaves of Pandanus, or Screw Pine, arranged in spiral
lines, contrast greatly in the Sandwich Islands with the finely divided
leaves of the Fern, spreading in graceful elegance, and trembling in the
breeze. Between these two extremes is the Palm-form, which gives most
characteristic beauty to the tropical world. Some Palms have feathered
leaves, others have fan-leaves, and in some of the umbrella Palms the
crown consists of a few fans elevated on long, slender stalks. In all
the inflorescence breaks from the stem below the origin of the leaves,
and the sheath hangs down, often several feet long. The shape and color
of the fruit varies from the large triangular Cocoa-nut to the berry of
the Date. The aerial summits of the Palms, projecting like a colonnade
above the thicket, and crowned with leaves, give them an air of
beautiful majesty. (Fig. 51.) Deciduous, or Leafy woods, (Fig. 61,) with
their branching stems and broad foliage, form dense, compact, vegetable
masses, characteristic of temperate climes. Wand-like forms, with
narrow, fluttering leaves, often covered with silvery down on the under
side, are represented by the Willow and Poplar, and in the south of
Europe by the Olive. The Conifers, or Needle-leaved woods, are
distinguished by their narrow, dark-green leaves and whorl-like
branches. (Fig. 59.) In the tropical or equinoctial regions the mass of
leafy woods is marked by the prevalence of the Mallow-form, with
long-stalked and palmately-lobed leaves. The giant Baobab, the
barrel-like trunk of the Bombax, and the purple-blossomed Hibiscus bush
belong to this class. The Australian Laurels and Myrtles are allied to
the northern Willows, yet their rigid leaves, shining as if varnished,
or covered with a silvery felt which mingles with the shining green,
give them a characteristic physiognomy.
Thus even a general observer may notice variety enough to indicate that
a free intelligence has arranged these forms to minister mental
enjoyment, as well as to supply the needs of intelligent creatures.
Archbishop Trench has well said that the characters of nature which
every-where meet the eye “are not a common, but a sacred writing—they
are hieroglyphics of God.”
CHAPTER XI.
P R O T O Z O A .
Since all bioplasm possesses certain common characters, and the
bioplasm of one plant or animal produces formed matter of a very
different kind from that resulting from another portion of
bioplasm, we must admit that in nature there are different kinds
of bioplasm.—DR. BEALE’S _Bioplasm_.
1. IN studying the structure of the Protozoa, or primitive animals, we
seem to be going backward, since each is composed of a single mass of
bioplasm, like the simplest vegetables, or Protophytes. Although similar
in structure, the Protozoa and the Protophytes are biologically distinct
in function, since the latter generally decompose Carbonic acid under
the influence of light, and generate Chlorophyll and albuminous
compounds in a manner similar to the leaf-cells of the most perfect
plant, while the Protozoa ingest and digest both animal and vegetable
food as effectively as the most complex animals.
We have already seen (Chap. II, Sec. 7) that all living matter, or
bioplasm, has essentially spontaneous motion, nutrition, growth, and
reproduction. We cannot conceive, therefore, of any form of life, either
vegetable or animal, without these characteristics. The simplest and
most embryonic structures in both kingdoms of nature exhibit these
functions. Whether spontaneous motion is proof of consciousness and
will, will be considered hereafter.
2. The MONERA of Prof. Haeckel, if the group shall be accepted by
naturalists, will include the simplest protozoans, or those in which the
entire living body is a mere particle of bioplasm, without nucleus,
vacuole, investment, or other structure, yet capable of bioplasmic
motions and other functions. _Bathybius_, referred to in Chap. IV, Sec.
3, was supposed to be of this class.
3. The GREGARINIDÆ are parasitic. Each consists of a single cell, which
passes through changes similar in many respects to Protophytes. It
becomes globular and encysted in a horny envelope, and the inclosed
bioplasm breaks up into particles which become “pseudo-navicellæ,” or
forms similar to the _Naviculæ_ of the family Diatomaceæ. It is not
unlikely that the _Gregarinæ_ are but phases in the life-history of
other parasitic worms.
4. RHIZOPODA. The Rhizopods, or root-footed Protozoans, (_rhiza_, a
root, and, _pous_, foot,) are characterized by the power of
spontaneously throwing out delicate processes of their bioplasm, called
_pseudopodia_, or false feet, for prehension or locomotion. They have no
cilia. Dr. Carpenter has divided the class into three orders: 1.
_Reticularia_, whose bodies are indefinite extensions of viscid
bioplasm, freely branching and subdividing into fine threads, but
readily coalescing when they come into contact. 2. _Radiolaria_, whose
bioplasm has an investing membrane of formed material which prevents the
coalescence of the radiating or rod-like extensions of the pseudopodia.
3. _Lobosa_, whose bioplasm has an investing membrane, or ectosarc, and
whose false feet are lobose extensions of the body itself.
[Illustration: FIG. 67.—Rosalina ornata, with its pseudopodia
extended.]
In the first order, that of reticularian rhizopods, we find many genera
and species which secrete a shell or external envelope of Carbonate of
Lime, or Chalk. These shells are often of singular beauty. They are
generally perforated by a large number of minute openings for the
passage of the pseudopodia, and hence are termed _Foraminifera_,
(_foramen_, an aperture; _fero_, I carry.) (Fig. 67.) Some of these
foraminifera are single chambers, often like striated flasks,
(_Lagena_,) but others are compound, either straight, (_Nodosaria_,)
spiral, (_Rotalia_,) or irregular, (_Globigerina_.) These shells are
generally microscopic, although some, as the _Nummulites_, may be an
inch in diameter, and the fossil _Eozoon Canadense_, which is referred
to this order, was of indefinite size. The Foraminifera accumulate in
the bed of the ocean in great numbers, yet in former ages they were
still more prolific, since the Chalk cliffs of England, the
building-stone of Paris, and the limestone of the Egyptian pyramids, are
composed of their remains.
[Illustration: FIG. 68.—Actinophrys sol, in different states. A. In its
ordinary sunlike form, with a prominent contractile vesicle, _o_. B. In
the act of division or of conjugation, with two contractile vesicles,
_o_, _o_. C. In the act of feeding. D. In the act of discharging fæcal
(?) matters, _a_ and _b_.]
In the Radiolarian order is placed the _Actinophryssol_,
(Sun-Animalcule,) (Fig. 68;) many species of _Polycystina_, which
secrete silicious shells, of various shapes and of wonderful beauty,
(Fig. 69;) and colonies of gelatinous rhizopods, (_Thalassicollida_,)
containing silicious spicules.
[Illustration: FIG. 69.—A. Podocyrtis Schomburgkii.
B. Rhopalocanium ornatum.]
To the order Lobosa belongs the _Amœba princeps_, (Fig. 2,) to which
reference has been so often made, since it has occupied so important a
position in modern biology. Chap. II, Secs. 2, 3, 5.
5. INFUSORIA, or Animalcules. The term Infusoria is applied to this
class because the species abound in any infusion of vegetable or even
animal matter which is allowed to putrefy. The word was formerly applied
to a much larger number of species than now, since many forms once
considered animal have been placed in the vegetable kingdom, as the
Desmids, the Diatoms, the Volvox, and many other Protophytes. The
Rotifers, or wheel-animalcules, also, on account of their organization,
are referred to the articulate type of animal life. It is possible that
some of the Infusoria may be but larval forms of higher animals. After
all this pruning, however, the class is still a large one, and full of
interest. It is divided into three orders: _Ciliata_, _Suctoria_, and
_Flagellata_.
Ciliated Infusoria (_ciliata_) are most numerous, and are named from the
cilia, or hair-like organs, round the mouth, or body, of the animalcule.
Cilia are not confined to animalcules. They are found among Protophytes,
(Chap. VI, Sec. 3.) They also exist in many organs of the higher
animals, as in the respiratory passages even of man himself. They appear
to be tapering prolongations of bioplasm, or of formed material in
connection with bioplasm, and have a sort of waving or circular motion.
In the internal organs of man their actions are constant, entirely
without consciousness, and may continue long after the death of the
body. In the animalcules the ciliary action is interrupted and renewed
in such a way as to impress an observer with the idea of choice and
direction.
_Vorticella_, or the bell-shaped animalcule, was described in Chap. I,
Sec. 6, and the life-history there given may serve for a representation
of the entire order.
_Epistylis_ differs from Vorticella in having a branching and
non-contractile stem.
_Vaginicola_ possesses a horny, cuticular case, (a _carapace_, or
_lorica_,) into which the animal can retire.
_Stentor_ is a fresh-water infusorian, shaped like a trumpet. It may be
found either free or attached.
_Paramecium_, (Fig. 70,) is a free, fresh-water animalcule, shaped like
a slipper, the hole for the foot being represented by the mouth.
[Illustration: FIG. 70.—Paramecium Aurelia, an Infusorian animalcule,
magnified 300 times.]
Suctorial Infusoria (order _Suctoria_) may be illustrated by the
parasitic _Acineta_, Chap. I, Sec. 6. They have filaments ending in
suctorial disks, which are capable of protrusion and retraction, and are
used for prehension.
The Flagellate Infusoria (order _Flagellata_) perform locomotion by
means of long filaments, or flagellæ, which may be single, double, or
multiple.
[Illustration: FIG. 71.—Noctiluca miliaris.]
The _Noctiluca_, (Fig. 71,) is the best-known member of this order. It
is very minute, about one eightieth of an inch in diameter, and presents
little more structure under the microscope than a simple sac of
bioplasm, with vacuoles, an oral aperture, and a tail of flagellum, but
at night these tiny beings light up the ocean with myriads of lamps,
whose phosphorescent property is yet a profound mystery.
The _Cercomonad_, an animalcule, with a long flagellum at each end, is
noted for the thorough investigations made by Messrs. Döllinger and
Drysdale. These gentlemen found it would increase for several days by
fission. Then it would lose the flagellæ and assume an amœboid form. Two
of these amœbiform Cercomonads would conjugate and become encysted, and
the rupture of the cyst gives exit to minute germs, which grow into the
original parent form. A temperature of 150° F. sufficed to destroy the
adult forms, but at 300° F. the germs still lived and developed. This
latter fact makes strongly against the theory of spontaneous generation.
6. SPONGES, (_Spongida_.) What we familiarly call a sponge is but the
skeleton of a colony of Protozoa. In this class a number of bioplasts,
whose individuality is still almost if not complete, are united
together, supported on a skeleton of horny, silicious, or calcareous
fibers united so as to form a net-work of tubes.
[Illustration: FIG. 72.—Sponge in action.]
In a living sponge currents of fluid set in through minute pores on the
surface, and come out in large streams through the larger apertures,
(_oscula_.) These currents are kept up by the cilia connected with the
bioplasmic masses which line the canals and cover the skeleton. By means
of these currents particles of food are brought within reach of the
bioplasts. (Fig. 72.) The Sponges are divided into three orders: Horny,
Silicious, and Calcareous sponges. In the first order (_Keratosa_) is
found the sponge of commerce, which owes its value to the fineness of
its fibers and the absence of silicious spicules. Some sponges of this
order have flinty spiculæ of various shapes, as pins, clubs, crosses,
hooks, and anchors. (Fig. 73.) The silicious sponges (_Silicea_)
sometimes have their spicules woven or fused together, as in the
beautiful _Euplectella_, or Venus’s Flower-basket. In _Hyalonema_, the
glass-rope, the long spicules, are twisted together.
[Illustration: FIG. 73.—_a._ Portion of Halichondria(?) from
Madagascar, with spicules projecting from the fibrous network. _b._
Silicious Spicules of _Pachymatisma_.]
In the order _Calcarea_ the skeleton is composed of Carbonate of lime.
Except a few fresh-water species, as _Spongilla_, sponges are marine.
The best sponges of commerce are from the Mediterranean.
7. The colonies of bioplasts in Thalassicollida and in Sponges are
analogous to the higher types of animal life, yet the individual cells
are so loosely bound together, and so capable of living and performing
all their functions apart, that they are ranked as Protozoa, as the
colonies of Volvocineæ, Nostochaceæ, and Confervaceæ, are placed among
the Protophytes.
8. The essential difference in the vital powers of different classes of
living things, and of the individuals of each class, is well exhibited
in the following passage from Johnston’s “British Sponges:” “For
example, it is very common to find growing on the same rock, or
sea-weed, a silicious, a calcareous, and a horny sponge; they have all
the same exposure, and are all recipients of the same nutriment, yet
does each act upon this differently. One extracts from the fluid silica,
which it causes to assume a solid crystalline form; another selects in
the same manner the calcareous particles, which, obedient to the laws of
life, assume figures novel to them in their mineral state; and again,
another rejects both the lime and the flint as injurious to its
constitution.”
CHAPTER XII.
R A D I A T A .
If we are astonished that so great deeds should proceed from the
little and low, it is because we fail to appreciate that little
things, even the least of living or physical existences in
nature, are, under God, expressions throughout of comprehensive
laws, laws that govern alike the small and the great.—DANA,
_Corals and Coral Makers_.
1. IN the simple Protophytes and Protozoa we find the essential
structure to be a single cell, or mass, of bioplasm, having in one
vegetable and in the other animal characteristics. In some instances
there is a colony, or association, of bioplasts, with certain mutual
relations; but as each bioplast is but loosely connected with the
others, and is capable of living and performing all its functions while
in a state of independence, these colonies are conveniently considered
among primordial types. In the higher forms of life, either animal or
vegetable, each individual is composed of many bioplasts, derived by
subdivision of the primitive mass. With the division of the structure
there is also a differentiation of function, so that no bioplasts of the
structure, save those which are appropriated to reproduction, can
normally pursue an independent existence.
2. The Radiate type of animal life is characterized by the idea
expressed in the word _radiation_. “In Radiates we have no prominent
bilateral symmetry, such as exists in all other animals, but an
all-sided symmetry, in which there is no right and left, no anterior and
posterior extremity, no above and below. It is true that in some of them
there are indications of that bilateral symmetry which becomes a law in
the higher animals; but whenever such a tendency is perceptible in the
Radiates it is subordinate to the typical plan on which the whole group
is founded.”[23]
3. Radiate animals are subdivided into I. CŒLENTERATA, or Cœlenterates,
(_koilos_, hollow; _enteron_, intestine,) or animals with an alimentary
canal communicating with the general cavity of the body; and, II.
ECHINODERMATA, (_echinos_, a spine; _derma_, skin,) or spiny-skinned
animals. Other characteristics, however, besides those signified in the
names of these sub-types are necessary to be considered.
4. The CŒLENTERATA are radiate animals with a distinct body-cavity,
whose walls consist of two layers of cellular tissue, an outer
(_ectoderm_) and inner, (_endoderm_,) and contain nettling thread-cells,
or small sacs full of fluid connected with barbed filaments, capable of
being projected for stinging purposes. Most of these animals have hollow
tentacles round the mouth. There are two large classes of Cœlenterates:
I. The HYDROZOA, which have no digestive cavity separate from the rest
of the mass which forms the body, and whose reproductive organs are
external; and, II. ACTINOZOA, which have a digestive canal distinct from
the rest of the body, suspended by radiating partitions, called
mesenteries; and whose organs of reproduction are internal, placed on
the mesenteries. The first of these classes may be represented by the
Hydra, and the latter by the Sea-anemone, or Actinia.
[Illustration: FIG. 74.—Hydra fusca, with a young bud at _b_, and a
more advanced bud at _c_. ]
The _Hydra_ is named after a fabled monster that reproduced its heads as
fast as they were cut off. The genus comprises two species, the green
and the brown Hydra, (_H. viridis_ and _H. fusca_.) (Fig. 74.) They are
minute creatures, about a quarter of an inch long, generally found on
the under surface of aquatic plants, attached by a disk, while their
long tentacles float downward in search of prey. The body is a simple
tube, or cavity, and the tentacles are supplied with “lasso-threads,” or
nettling thread-cells. In the early summer small buds grow from the base
of the body, which grow into the likeness of the parent, and then are
detached. Sometimes a second crop of buds arise from the first before it
is separated. Later in the season eggs form from modified cells of the
inner layer, which burst through the outer layer, become free, and
develop into new Hydræ.
These animals are nearly allied to the Protozoa, since the
differentiation of function in the bioplasts is incomplete. Hence the
wonderful powers of propagation in these creatures, which have
astonished naturalists ever since Trembley first discovered them, in
1744. He says: “I have opened a polyp on my hand, extended it, and cut
the simple skin of which it is formed in every direction; I have reduced
it to little pieces, and, in a manner, minced it. These little pieces of
skin, both those which did and those which did not possess arms, became
perfect polyps.” Many curious multiple forms have been produced by
experiments on these animals. By slitting the body into two branches,
and these branches again into others, a tree-like form may be produced,
each branch giving rise to a distinct head and tentacles. Or one may be
turned inside out like a glove, so that the outer skin becomes the
lining of the stomach-cavity, with a transposition of the functions of
each.
_Order 1._ _Hydroida._ This order is composed of animals built on the
pattern of the Hydra, just described. They are either single, as the
Hydra, or compound. The latter are subdivided into the three families of
Campanularians, Sertularians, and Tubularians. They are grouped in
clusters or colonies on a common axis or stalk, (_cœnosarc_.) Each
hydra-like organism is called a _polypite_. New polypites arise as
outgrowths from the common stem of the colony, so that the stomach of
each is continuous with the tubular center of the stalk, producing a
community of nutrition in the colony. In Chap. III., Sec. 14, reference
was made to the alternation of generations which this order of animals
so strikingly illustrates. This process in the life-history of the
Hydroids is briefly as follows: The Polyp, a fixed animal, increases for
awhile by budding, but at a certain period gives birth, by subdivision,
to free swimming Medusæ, or Jelly-fish. Each of these, after pursuing
for a time its own course of life and development, produces eggs which
change into ciliated bodies (_Planula_) similar to some of the
Infusoria. After a while each of these becomes stationary, fixes itself
to some weed or rock, and becomes a polyp, or Hydroid.
Those Medusæ which swim by the contraction of their umbrella-like disk
were formerly called _Pulmogrades_; those which swim by vibratile cilia
attached to arms, _Ciliogrades_; those which float by an expansive
bladder, _Physogrades_; and those furnished with arms, or cirri,
_Cirrigrades_. Another classification divided them into “naked-eyed” and
“hidden-eyed” Medusæ. Since more thorough research has shown their
relation to the Hydroids, the Medusæ have been considered in reference
to the families of Hydroids from which they spring.
The _Tubularian_ family (_tubulus_, a little tube) consist of Hydroids,
sometimes simple, but generally compound, united by a common trunk or
cœnosarc, which has an external horny coat, or _polypary_. Sometimes the
tube is jointed with the tentacles placed in a whorl round each joint,
(_Tubularidæ divisa_,) sometimes it is undivided, (_T. indivisa_.)
Sometimes the polypary is much branched, (as in _Eudendrium_,) but in
the majority it is not branched. A few species have no hard polypary,
(as _Corymorpha nutans_,) but simply a white fleshy stem. The polyps of
this family have no protecting cups. The Medusæ bud from the stem.
The _Sertularian_ family (_Sertula_, a little wreath) is generally
regarded as a sea-weed by sea-side visitors, but a very cursory
examination with a pocket lens will suffice to show the horny and
branched polypary, with its little cups, (_hydrothecæ_,) which contain
and protect the polypites. In some of the Sertularians the Medusæ
wither on the stock, never becoming free.
The _Campanularian_ family (_Campanula_, a little bell) resemble
Sertularians, except that the cups (_hydrothecæ_) are stalked and
terminal instead of being lateral and sessile, as in the latter. The
reproductive calyces, or ovarian capsules, may contain many Medusæ buds
developed one below the other, which are set free by the bursting of the
cell. (Fig. 75.)
[Illustration: FIG. 76.—Development of Sarsia. 1. Polyps described as
Syncoryne, natural size. 2. A polyp, magnified. _a._ Polyp stem. _b._
_c._ _d._ _e._ Medusoid buds, in various stages. _f._ Tentacles of the
polyp. 3. Free Medusa of the genus _Sarsia_. ]
The ordinary Jelly-fish (_Medusa_, or _Acaleph_) is soft, gelatinous,
and bell-shaped, with tubes radiating from center to circumference,
where they connect with a circular canal. The margin is fringed with
stinging tentacles. The radiating parts are in multiples of four. These
gelatinous bells, varying from the size of a pea to a foot or more in
diameter, float, mouth downward, in the sea, and propel themselves by
flapping their sides. (Fig. 76.) There are two representative forms of
Medusæ, the _Lucernaria_, or Umbrella-acaleph, attached by a short
pedicle, and having tentacles disposed in eight groups around the
margin, and not less than eight radiating canals; and _Discophora_, the
ordinary Jelly-fish, free and oceanic, with four radiating canals in the
disk, which ramify and open into a circular canal around the mouth of
the disk.
[Illustration: FIG. 77.—Physalia. ]
_Order 2._ _Siphonophora_, or floating Hydroids, (_siphon_, a curved
tube, and, _phero_, to bear,) are free swimming or compound floating
Hydroids, with an unbranched, or slightly branched, but muscular
cœnosarc. The common stem of these colonies swims by means of enlarged
and altered polyphites, whose stomachs are undeveloped and whose bodies
are dilated. Some possess, also, a sac filled with air, which acts as a
float, as the _Physalia_, (_physa_, a bubble,) or Portuguese Man-of-war,
whose purple-crested air-sac and long tentacles attract such attention
in tropical seas, and whose thread-cells inflict such painful stings
when grasped by an incautious hand. (Fig. 77.) The _Porpita_ (_porpe_,
the ring of a shield) possesses an internal skeleton, or flat plate, of
cartilaginous texture, which is cellular and lighter than water. Its
lower surface contains a beautiful fringe of blue tentacles, or cirri.
In the _Velella_ (_velella_, a little sail) a second cartilaginous plate
rises nearly at right angles from the upper surface of the horizontal
one, serving as a sail to waft the little mariner from place to place.
CLASS II. ACTINOZOA, (_actin_, a ray; _zoon_, an animal.) This class
embraces the Sea-anemones, the Corals, and the Ctenophora, (_kteis_, a
comb; _phero_, I bear,) or comb-bearing Medusæ. The digestive cavity is
suspended in the body cavity, like a small bag within a larger one, by
vertical partitions, some of which extend from the body-wall to the
digestive sac, but others fall short of it. Upon these septa, or
mesenteries, are the organs of reproduction. The ectoderm is more highly
developed than in Hydrozoa, and both mesenteries and body-walls are
supplied with distinct sets of muscles. Cilia are present on the
digestive tube, producing a current both respiratory and circulatory.
[Illustration: FIG. 78.—A. Sea-anemone, seen from above. B. Section of
Sea-anemone. _a._ Cavity of stomach. _b._ Surrounding chambers. ]
The _Actiniæ_, or Sea-anemones, are the much-admired forms so often seen
in the rock-pools around our shores, sometimes called animal flowers,
attached to the rocks by a flat disk, expanding their petal-like
tentacles in search of prey, and, when uncovered by the retreating tide,
contracting into small round gelatinous masses. The tentacles and
partitions of the body are in multiples of six. Fig. 78 represents the
internal form of Actinia.
[Illustration: FIG. 79.—Corals.]
The _Coral polyps_ are Actinozoa, which secrete coral, generally
composed of carbonate of lime, but it is occasionally horny, or a
mixture of horny and calcareous matter. These polyps are usually found
in colonies formed by a continuous process of budding. The compound mass
is like a sheet of animal matter, fed and nourished by numerous mouths
and many stomachs. Corals are of two kinds, the sclerobasic and
sclerodermic corals. The polyps of the latter resemble Actiniæ in
structure. The earthy matter is secreted between each pair of
partitions, so that the skeleton of a single polyp (or _corallite_) is a
short tube with vertical septa radiating toward the center.
[Illustration: FIG. 80.—Madrepore.]
The _Fungia_, or Mushroom coral, is disk-shaped, and differs from others
in not being either fixed or compound. It is simply the skeleton of a
single polyp, showing a radiating secretion of calcareous septa. The
various kinds of budding in compound coral-polyps give rise to a variety
of shapes, either dome-like or branching. _Astræa_ is a hemispherical
mass covered with large cells. _Meandrina_, or “Brain-coral,” has the
mouths of the polyps opening into each other, forming furrows. (Fig.
79.) _Madrepore_ branches, like a tree, with pointed extremities. (Fig.
80.)
[Illustration: FIG. 81.—1. Sea-fan. 2. Sea-pen.]
Sclerobasic corals are those which secrete coral by the outer layer of
the inverted ectoderm. Most of these are of the order _Alcyonaria_,
whose polyps are characterized by primate or fringed tentacles in
multiples of four, while the sclerodermic corals generally belong to the
order Zoantharia, with polyps having simple tentacles in multiples of
five or six. The characters of Alcyonarian polyps may be seen by placing
in sea-water some of those large yellowish, gristly masses, sometimes
cast up by the sea, known as “dead men’s fingers.” From the surface of
each pore the tentacles round the mouth of the polyps will protrude,
showing, their general resemblance to Actinia. Minute spicules of
calcareous matter are scattered throughout the mass.
[Illustration: FIG. 82.—Red Coral.]
[Illustration: FIG. 83.—Tubicora Musica.—Organ-pipe Coral.]
In _Gorgonia_ such spicules, with horny matter, make up a continuous
branching coral in the same plane, whose ramifications unite in a
beautiful net-work. (Fig. 81.) In _Corallium rubrum_, the precious coral
of commerce, the axis is of stony hardness, and branching like a shrub.
In the living state the branches are covered with a red cœnosarc,
(common flesh,) studded with polyps. (Fig. 82.) The feather-shaped
sea-pens (_Pennatula_) have the extremities of their stems buried in
sand. In some genera, as _Virgularia_, the stem is prolonged to between
three and four feet in length, while the polypiferous lobes are
comparatively short. The red organ-pipe coral of the Indian Ocean, (Fig.
83,) with its table-like partitions and green polyps, belong also to
this group.
[Illustration: FIG. 84.—A Coral Island.]
The work of the reef-building polyps is extremely interesting. They will
not live in water whose mean temperature is below 68° F., nor at a
greater depth than twenty fathoms, yet coral reefs are constantly found
which are several hundred fathoms thick. This apparent paradox is due to
the fact that the land where coral reefs are forming is constantly
subsiding, and fresh living corals are taking the place of the dead
ones. If the center of a reef sinks more quickly than the sides a lagoon
is left, surrounded by a circular reef of coral, called an atoll; if an
island rises in the middle of this lagoon a barrier reef is said to be
formed, (Fig. 84;) while if the sea clearly intervenes between the reef
and the mainland, we have what is termed a “fringing reef.” Different
species of polyps build these reefs. Madrepores, Millepores, and
Gorgonidæ work chiefly at the top, next below we meet with Meandrinas,
and lowest of all, with Astræans.
The _Ctenophoræ_, or comb-bearing Medusæ, exhibit traces of a nervous
system in a ganglionic mass at the upper end, or pole, of the animal,
with nervous filaments radiating to every part of the body. They are
transparent gelatinous animals, which swim freely by means of bands of
comb-like fringes or paddles. Their internal structure is quite complex,
having a distinct alimentary canal, and ducts for the circulation of
fluid. They are retained in the Radiate type, on account of the radiate
arrangement of the bands of cilia and the presence of urticating organs
on the tentacles, although their affinities would seem to place them
elsewhere.
[Illustration: FIG. 85.—A. Cydippe pileus, with its tentacles extended.
B. Beroë Forskalii, showing the tubular prolongations of the stomach. ]
The _Beroë_ and _Cydippe_ (Fig. 85) and _Cestum Veneris_, or Girdle of
Venus, belong to this order. In the latter, the sides are prolonged into
a ribbon, although the mouth and digestive organs are confined to the
middle of the body. In the day-time its waving cilia along the margins
of the body glitter with the tints of the rainbow, and at night it
appears like a long waving flame in the water.
5. The subtype of Radiate animals, called ECHINODERMATA, is
distinguished by the possession of a nervous system, in the form of a
pentagonal ring round the mouth; an alimentary canal, with oral and anal
apertures; a peculiar system of circular and radiating canals; and a
symmetrical arrangement of all the parts of the body around a central
axis, in multiples of five. Some star-fishes (_Solaster_) have twelve
rays. In all Echinoderms, probably, sea-water is freely admitted into
the body-cavity around the viscera. The canals likewise contain water,
which enters through a porous tubercle, the _madreporic plate_, or
dorsal wart, best seen on the back of the star-fish and the sea-urchin.
Some naturalists rank Echinoderms as Worms.
The _Crinoidea_, or Sea-lilies, so called from their resemblance to
flowers, are fixed to the sea-bottom by a hollow, jointed, flexible
stem, which carries the body, which is cup-shaped, with radiating arms,
or tentacles. This order includes an immense number of fossil forms, but
deep-sea dredging has brought up many living species, formerly thought
to belong exclusively to the Mesozoic period. They all possess an
internal skeleton of infiltrated calcareous matter, so that the entire
animal consisted of thousands of stellate pieces, or joints, connected
by animal matter. As each joint is furnished with at least two bundles
of muscular fiber, one for extension and one for contraction, Dr.
Carpenter estimates three hundred thousand such muscles in a single
_Pentacrinus_—an amount of muscular apparatus far exceeding any that
has been elsewhere observed in the animal creation. The family,
COMATULIDÆ, or Hair-stars—sometimes termed Feather-stars—in their
young condition, resemble the _Encrinites_, or Sea-lilies, being
supported on a long flexible stalk, composed of calcareous cylinders. At
maturity they quit their attachment, and crawl about like other
Star-fishes.
The order ASTEROIDEA, or Star-fishes, consists of animals with a flat
central disk, having five or more arms, or lobes, radiating from it, and
containing branches of the viscera. The skin is leathery, hardened by
small calcareous plates, (eleven thousand or more,) but somewhat
flexible. The mouth is below, and the rays are furrowed underneath and
pierced with numerous holes through which pass sucker-like tentacles for
locomotion and prehension. These furrows are named _ambulacra_, or
avenues, from a fancied resemblance to a walk, or alley, in a garden. As
the tentacles, or suckers, are only protruded from these spaces, they
also have been called _ambulacra_. The arrangement for their protrusion
will be described in connection with the Sea-urchins, as well as the
_Pedicellariæ_ (formerly believed to be parasitic organisms) found near
the mouth.
[Illustration: FIG. 86.—Ophiura.]
About one hundred and fifty species of Star-fishes are known, divided
into three groups: (1.) those having four rows of feet, as the common
five-fingered Star-fish, or _Asterias_; (2.) those with two rows, as the
many-rayed _Solaster_, or Sun-fish, and the pentagonal _Goniaster_; (3.)
those with long slender arms, which are not prolongations of the body,
and are not provided with suckers, as the _Ophiura_, or Brittle-star,
(Fig. 86,) and _Asterophyton_, or Basket-fish. The last group are
inferior in structure, and resemble inverted stemless Crinoids. The
digestive sac is confined to the disk, and the madreporic plate is
underneath.
[Illustration: FIG. 87.—Morphology of Echinoidea. 1. Echinid larva.
_a._ Mouth. _b._ Stomach. _c._ Intestine. _s._ Skeleton. 2. Diagram of
Echinus. The spines and the ambulacra are represented over a small
portion of the test; the vascular system is cross-shaded; the nervous
system is represented by the black line. _a._ Anus. _b._ Stomach. _c._
Mouth. _d_ and _f._ Vascular rings round the alimentary canal. _e._
Heart. _g._ Test. _h._ Nervous ring round the gullet. _i._ Ambulacral
ring, or circular canal round the gullet. _k k._ Polian vesicles. _l._
Sand canal. _m m._ Radiating ambulacral canal. _n._ Secondary ambulacral
vesicles. _o._ Ambulacra, or “tube-feet.” _p._ Spines. _r._
Madreporiform tubercle. ]
The order ECHINOIDEA, or Sea-urchins, contains those Echinoderms whose
skin secretes calcareous plates, forming a hollow shell, covered with
spines, and varying in shape from a sphere to a disk. The shell of an
_Echinus_ is made up of twenty rows, or zones, of plates, of which five
pairs are ambulacral, pierced with minute pores for the protrusion of
ambulacra, or sucker-feet, and five pairs alternating with the former
are inter-ambulacral. The shell is developed from a membrane which lines
the interior of the plates, and passes between the joints, so that
additions can be made to their edges, by which means the shell grows and
preserves the same relative proportions. The upper end of the shell, in
addition to five small circularly disposed plates, carries five large
genital plates. Each of these has a duct for the passage of ova or
spermatozoa, and an _ocellus_, or eye-spot. One of these plates is the
madreporic tubercle, with minute apertures communicating with the
madreporic canal. Locomotion is effected by the hollow muscular feet,
each of which communicates with a water sac; they also communicate with
each other, so that as each sac contracts, water is forced into the
corresponding tube, which is thereby elongated and protruded. (Fig. 87.)
[Illustration: FIG. 88.—Shell of Echinus, or Sea-urchin; on the right
side, covered with spines; on the left, the spines removed. ]
The shell of the Echinus is covered with semi-globular warts, or beads,
each of which during life supports a sculptured spine with a hollow at
its base, forming with its muscles and ligaments a ball and socket
joint, subsidiary to locomotion. (Figs. 88 and 89.) _Pedicellariæ_ are
minute, almost microscopic, jointed spines, scattered all over the shell
of the Echinus, and terminated by a three-fold claw, capable of being
closed like a pair of forceps upon animalculæ or other offensive matter
that may tend to obstruct its shell. One carries the rejected matter to
another till the surface is completely free.
[Illustration: FIG. 89.—Morphology of Echinoidea. 1. Portion of the
test of Galerites hemisphericus enlarged, showing the inter-ambulacral
area (_a_) and the ambulacral areas, (_b_.) 2. Galerites hemisphericus
viewed from above. _a._ Inter-ambulacra. _b._ Ambulacra. 3. Genital and
ocular disk of Hemicidaris intermedia, enlarged. _c._ Ocular plate. _d._
Genital plate. _e._ Anal aperture. _f._ Madreporiform tubercle. 4. Spine
of the same. (After Forbes.) The tubercles are mostly omitted on figs. 2
and 3 for the sake of clearness. ]
[Illustration: FIG. 90.—Dentary Apparatus of Echinus, or Aristotle’s
Lantern. The right-hand diagram shows three of the teeth in position.
_a a._ Cutting edges of the teeth, which are extremely hard. _b._
Fibrous roots of the teeth. _c c._ Opposed bony surfaces of the jaws.
_d d._ Arched processes. The left-hand diagram shows an isolated
pyramid. _e._ External surface. Other letters as before. ]
The mouth of an Echinus contains the most complex and perfect dental
apparatus in all the Animal Kingdom, although occurring in a type
generally considered of a low grade of structure. It sets at naught all
theories of Evolution, since in our progress from the simplest forms of
life it is the first instance of a dental apparatus, and the most
perfect of all. It is composed of five accurately-fitting vertical
pyramids, each provided with a rod-like tooth, worked by a couple of
beautifully arranged muscles. (Fig. 90.) The intestine is tortuous and
connected by delicate mesenteries to the shell. These animals possess a
heart with an aorta surrounding the gullet and intestine. The blood is
aërated by exposure to the oxygen mixed with the water which is
constantly circulating over the vascular mesenteries.
[Illustration: FIG. 91.—Embryonic development of Echinus:—A. Pluteus
larva at the time of the first appearance of the disk. _a._ Mouth in the
midst of the four-pronged proboscis. _b._ Stomach. _c._ Echinoid disk.
_d d d d._ Four of the Pluteus body. _e._ Calcareous frame-work. _f._
Ciliated lobes. _g g g g._ Ciliated processes of the proboscis. B. Disk,
with the first indication of the cirrhi. C. Disk, with the origin of the
spines between the cirrhi. D. More advanced disk, with the cirrhi and
spines projecting considerably from the surface. (N.B. In figs. B, C,
and D, the Pluteus is not represeuted, its parts having undergone no
change, save in becoming relatively smaller.) ]
The metamorphosis of Echinus is very curious. The embryo is a free
swimming minute ciliated creature, strangely like a painter’s easel, and
hence called a _Pluteus_. [_Pluteus_, a penthouse.] This passes through
a strange cycle of changes. The digestive canal appears in the middle of
the frame, which gradually disappears, the future Echinus is sketched
in, and a radially symmetric animal results, totally unlike its
predecessor. (Fig. 91.)
Regular Echini, as the common _Cidaris_, are nearly globular, and the
oral and anal openings are opposite. Irregular Echini, as the
_Clypeaster_ and _Spatangus_, are flat, or discoid, with hair-like
spines, and the rows of ambulacra form a five-rayed star on the back of
the shell. _Spatangus_ has no dental apparatus.
The order HOLOTHUROIDEA, embraces what are commonly known as Sea-slugs,
Sea-cucumbers, or Trepangs. The body is elongated and soft, with a tough
contractile skin containing calcareous spicules. One end, the head, has
a simple aperture for a mouth, encircled with feathery tentacles. In the
_Holothuriæ_ proper, locomotion is effected by rows of ambulacral
tube-feet, but in the _Synaptidæ_ there are no ambulacra, and the animal
moves by means of anchor-shaped spiculæ which are scattered in the
integument. Animals of this order have the singular power of ejecting
all of their internal organs, surviving the loss if these parts, and
afterward reproducing them. There vermiform larva has no skeleton.
6. The Radiate type of animal life well illustrates the intellectual
plan, or typical design, of living forms, and contains many instances
totally unaccountable on any scheme of material gradation whatever. The
nettling thread-cells, or _Cnidæ_ in the Hydroids, the peculiar
alternation of generations in the Medusæ, the great amount of muscular
development in the Crinoida, the pedicellariæ, and the dental apparatus
of Echinus, are all examples of structural arrangement for a purpose,
and make against the theory of evolutional development, or survival of
the fittest. Each of these structures are the most perfect of their
kind, and seem to have no previous structure from which they have
developed, as they have left no succeeding apparatus analogous or
homologous to them.
CHAPTER XIII.
M O L L U S C A .
I have seen
A curious child applying to his ear
The convolutions of a smooth-lipped shell,
To which, in silence hushed, his very soul
Listened intensely, and his countenance soon
Brightened with joy; for murmuring from within
Were heard sonorous cadences whereby,
To his belief, the monitor expressed
Mysterious union with its native sea.
—WORDSWORTH.
1. The type of Mollusca, or soft-bodied animals, is indicated by the
name, derived from the Latin _mollis_, soft. Like other types it
embraces species of various degrees of complexity of structure, and of
various forms. It includes soft-bodied, unjointed animals, possessing a
muscular skin, or mantle, generally protected by a calcareous shell, and
whose nervous system is scattered. It is subdivided into 1. MOLLUSCOIDA,
containing the classes _Polyzoa_, _Tunicata_, and _Brachiopoda_; and 2.
TRUE MOLLUSCA, embracing the classes _Lamellibranchiata_, _Gasteropoda_,
and _Cephalopoda_.
[Illustration: FIG. 92.—Sea Mat, (_Flustra foliacea_.) A. Magnified. B.
Natural size. ]
2. POLYZOA (Gr. _polus_, many, and _zoon_, animal) derive their name
from the fact of their living in clusters or colonies. They are
sometimes called _Byozoa_, (Gr. _byon_, moss, and _zoon_, animal,) or
Sea-moss. They greatly resemble the Hydroid polyps, but from the greater
complexity and character of their organization they have been removed to
this type. The cells of a group are not connected with a common tube, as
in Cælenterates, and each animal possesses a distinct alimentary canal
and nervous system. Sometimes the colonies are foliaceous, or leaf-like,
as the Sea Mat, _Flustra_, (Fig. 92,) and at others plant-like, as the
_Plumatella_. (Fig. 93.) They sometimes spread over rocks and sea-weeds
like delicate lace-work, and the majority are coral-making animals, or
secrete carbonate of lime. The mouth of each animal is surrounded by
ciliated tentacles which serve for prehension, circulation, and
respiration. Many species are furnished with organs of a remarkable and
peculiar kind, called _Avicularia_, (_avicula_, a little bird,) or
“bird’s heads,” which during life, and even after the death of the
animal, keep up a continual motion, see-sawing, and snapping, and
opening their jaws in the most singular manner. Their use is unknown,
but Mr. Gosse conjectures that they may seize and hold minute animals
until decomposition attracts a crowd of Infusoria, which may serve the
Polyzoan for food. Some species of Polyzoa are found in fresh water.
[Illustration: FIG. 93.—Plumatella. _a._ Natural size. _b._ A group
enlarged. _c._ Anal orifice. ]
3. TUNICATA, named from the Latin _tunica_, a cloak, is a class of
Molluscoida which are enveloped in a tough, leathery sac, or “test.”
This sac is double-walled, but not capable of protrusion. The mouth of
the animal opens into the bottom of a respiratory sac whose walls are
lined by a net-work of blood-vessels. The tubular heart exhibits the
curious phenomenon of reversing its action at brief intervals, so that
the blood oscillates backward and forward in the same vessels. The wall
of the tunic contains cellulose, which is generally a vegetable product.
[Illustration: FIG. 94.—A. Group of Perophora, (enlarged,) growing from
a common stalk:—B. Single Perophora. _a._ Test. _b._ Inner sac. _c._
Branchial sac, attached to the inner sac along the line _c'. c'._ _e._
_e._ Finger-like processes projecting inward. _f._ Cavity between test
and internal coat. _f'._ Anal orifice or funnel. _g._ Oral orifice.
_g'._ Oral tentacula. _h._ Downward stream of food. _h'._ Œsophagus.
_i._ Stomach. _k._ Vent. _l._ Ovary. (?) _n._ Vessels connecting the
circulation in the body with that in the stalk. ]
These bottle-shaped creatures are found in the ocean, “solitary,”
attached to rocks or sea-weed, and often glued together in bunches.
Sometimes they are in “social” groups, as in Fig. 94, or “compound,” as
Fig. 95.
[Illustration: FIG. 95.—Botryllus violaceus: A. Cluster on the surface
of a Fucus. B. Portion of the same enlarged. ]
The _Salpæ_ are free swimming, transparent _Ascidians_, (_askos_, a bag;
_eidos_, like,) or Tunicates, often found adhering to each other in long
chains, which give birth to solitary individuals of different form by
alternation of generations.
Young Tunicata swim, like tadpoles, by a tail, which contains a peculiar
rod-like body, consisting of nucleated cells like the _chorda dorsalis_,
or _notochord_; an elongated mass of cells in the Vertebrate embryo,
which is afterward replaced by the vertebral column. From this
resemblance the partisans of evolution have claimed that this simple
cellular structure is the prototype of that which distinguishes the
higher animals, and that from the simple Ascidian the Vertebrate has
been developed. Such foreshadowings of higher types is not uncommon. It
will require, however, much greater evidence to prove transmutation than
such resemblances.
4. BRACHIOPODA are protected by a bivalve shell, which is lined by an
expansion of the integument, or “mantle.” The valves of the shell are
applied to the dorsal and ventral sides of the body. The ventral valve
is usually larger and more convex than the other; but they are
symmetrical, that is, a vertical line from the hinge divides the shell
into equal parts. The ventral valve generally has a hole, or _foramen_,
through which a fleshy foot protrudes for attachment. The mouth is
furnished with two long arms, fringed with cirri, generally coiled up
and supported by a bony frame-work in the shell—the “carriage-spring
apparatus.” As there are no gills, the animal respires by the arms or
the mantle. Brachiopods were once very abundant, over two thousand
extinct species having been described; but less than one hundred species
are now living.
In all the Molluscoida the nervous system consists of a single ganglion,
or of a principal pair with accessory ganglia placed between the oral
and anal apertures, or on the ventral surface of the body. Some
naturalists connect them with the Worms.
5. LAMELLIBRANCHIATA (Lat., _lamella_, a plate; Gr., _bragchia_, gill)
comprise the ordinary bivalves, as the Oyster, Mussel, and Clam, and are
characterized by the possession of lamellar gills. The shells differ
from those of Brachiopods in being placed on the right and left sides of
the body, so that the hinge is on the back of the animal, and in being
generally unequilateral and equivalved. They are sometimes termed
CONCHIFERA, or shell-fish, (Lat., _concha_, a shell; _fero_, I carry.)
The shells of Mollusks are epidermal structures. The mantle, or loose
skin, secretes calcareous matter in layers, converting the epidermis
into shell. The microscopic structure is so characteristic that a thin
section of a fragment often suffices to determine the group to which it
belongs. A large class of shells is formed like the Oyster, of three
parts; the external epidermis, brown and of a horny texture; the
prismatic portion, consisting of minute columns set perpendicularly to
the surface; and the internal nacreous, or pearly layer, made up of very
thin plates whose edges overlap and form wavy lines. In many cases the
prismatic and pearly layers are traversed by minute tubes. The pearls of
commerce, found in the mantle of some Mollusks, are similar in structure
to the shell; but what is the innermost layer in the shell is outside
and much finer in the pearl, which is formed around some nucleus, as an
organic particle or grain of sand.
[Illustration: FIG. 96.—_a._ _b._ Length of the shell. _c._ _d._
Height. _e._ Lunula, above which is the summit. _d._ The ventral or
inferior edge. ]
Shells of one piece are called “univalves,” as the snail. Others, as the
Clam, are of two parts, and are called “bivalves.” The ribs, ridges, and
spines on the outside mark successive periods of growth, and correspond
with the age of the animal. Figs. 96 and 97 show the principal parts of
ordinary bivalves and univalves. The valves of a bivalve are generally
equal, except in Brachiopods and in the Oyster. The umbones, or beaks,
are a little in front of the center, and turn toward the mouth of the
animal. The valves are joined by a ligament near the umbones, and often
also by a “hinge” formed by the “teeth” of one valve locking into
cavities of the other. The aperture of a univalve is sometimes closed by
a horny or calcareous plate, called an “_operculum_.”
[Illustration: FIG. 97.—A. The line across marks the thickness of
bivalves. B. _a._ Anterior extremity. _b._ Posterior. _c._ _d._ Muscular
impressions. _e._ _f._ Palleal impression. _g._ Lower edge of the left
valve. ]
[Illustration: FIG. 98.—Diagrammatic Transverse Section of Anodon,
through the heart. _a._ _a._ Lobes of mantle. _b._ _b._ Gills, showing
transverse partitions. _c._ Ventricle of heart. _d._ _d._ Auricles. _e._
Pericardium. _f._ Glandular sac of organ of Bojanus. _g._ Vestible, or
middle sac. _h._ Venous sinus. _k._ Foot. A. A. Branchial or pallial
chamber. B. B. Epibranchial chamber, communicating with cloaca. ]
Lamellibranchs breathe by four plate-like gills, two on each side,
underneath the mantle. (Fig. 98.) In the higher forms the mantle is
rolled up into two tubes, or siphons, for the inhalation and exhalation
of water. The mouth opens into the stomach, which lies imbedded in a
large liver, and the intestine, after a few turns, passes directly
through the heart (Fig. 99.) The nervous system consists of three pairs
of ganglia, and the heart has two chambers, an auricle and ventricle,
and, in some cases, two auricles and a ventricle. The ventricle propels
the blood into the arteries, by which it is distributed through the
body. From the arteries it passes into the veins, and is conducted to
the gills, where it is aërated, and is finally returned to the auricles.
[Illustration: FIG. 99.—Anatomy of a bivalve Mollusk, (Mactra.) _a._
Shell-muscles. _b._ Ganglia. _c._ Heart. _d._ Liver. _e._ Mouth. _f._
Labial tentacles. _g._ Foot. _h._ Stomach. _i._ Intestine. _k._ Anus.
_m._ Mantle. _n._ Branchiæ. _o._ Base of inhalent siphon. _p._ Base of
exhalent siphon. ]
A few Lamellibranchs are fixed, as the Salt-water Mussel, which hangs to
the rocks by a cord of threads called “byssus,” and the Oyster, which
habitually lies on its left valve; but the rest have a foot by which
they creep about. There are more than four thousand living species,
fresh water and marine, which range from the line of shore to the depth
of a thousand feet.
The muscular impressions on the shell, (_c._ _d._, Fig. 97;) the
presence of a pallial sinus, _e._, which indicates the possession of
siphons; the structure of the hinge, and the symmetry of the valves, are
the chief characters for distinguishing genera and species of this
class, which has been divided into groups, based on the possession or
non-possession of siphons, as follows:
Section A. _Asiphonidæ._ Without respiratory siphons, so that the shell
shows the pallial line simple, and not indented. As in the families of
Oysters, (_Ostreidæ_,) Mussels, (_Mytilidæ_,) Wing-shells, or Pearl
Oysters, (_Aviculidæ_,) and River Mussels, (_Unionidæ_.)
Section B. _Siphonida._ Having siphons.
(1.) _Integro-pallialia._ Siphon short, pallial line simple, as in the
families _Tridacnidæ_, _Cardiadæ_, (Cockles,) and _Cyprinidæ_,
(Heart-cockles.)
(2.) _Sinu-pallialia._ Long siphons, pallial line sinuated, as in
_Veneridæ_, (Clams,) _Mactridæ_, _Solenidæ_, (Razor-shells,) and
_Pholadidæ_, (Boring-shells.)
6. GASTEROPODA, (Gr., _gaster_, stomach; _pous_, foot.) This class
derives its name from the fact that locomotion is usually effected by a
muscular expansion of the under surface of the body, termed the “foot.”
It includes all the univalve shells, the naked slugs, the Dorsibranchs,
the Pteropods, and the Multivalvular Chiton.
The body of most Gasteropods is unsymmetrical, the organs not being in
pairs, but single, and on one side, instead of central. The mantle is
continuous round the body, not bilobed, as in Lamellibranchs. A few, as
the Garden-snail, have a lung, but the majority breathe by gills. The
head is more or less distinct, and is provided with two tentacles, with
auditory sacs, or rudimentary organs of hearing at their bases. The eyes
are sometimes quite conspicuous. The Snail, for example, carries two
_ocelli_, or simple eyes, on the tip of its long tentacles. Each
consists of a globular lens, of short focus, which is a part of the
transparent cornea, with a colored membrane (choroid) and a nervous
net-work (retina) behind. The arrangement for retracting the eye and
tentacle is seen in Fig. 100.
[Illustration: FIG. 100.—Head of a Snail bisected, showing structure of
tentacles: _a._ Right inferior tentacle retracted within the body. _b._
Right superior tentacle fully protruded. _c._ Left superior tentacle
partially inverted. _d._ Left inferior tentacle. _f._ Optic nerve. _g._
Retractor muscle. _h._ Optic nerve in loose folds. _i._ Retractor muscle
of head. _k._ Nerve and muscle of left inferior tentacle. _l._ _m._
Nervous collar. ]
[Illustration: FIG. 101.—Palate of Buccinum undatum, as seen under
polarized light. ]
The mouth of Gasteropods possesses a peculiar strap-like organ, the
_odontophore_, (_odous_, tooth; _phero_, I bear.) It is studded with
three or more rows of lingual teeth, formed of silica, which are the
serrated edges of minute plates, the number of which varies in different
species; the garden Slug has one hundred rows with one hundred and
eighty teeth in each row. (Fig. 101.) The strap, or “tongue,” plays over
a cartilaginous cushion, or pulley, connected with the lower jaw, and
the teeth are renewed by fresh growths from the membrane beneath. The
gullet is long, and frequently expands into a crop; the stomach is often
double, the anterior being a gizzard provided with teeth for
mastication; the intestine passes through the liver, and ends in the
fore part of the body, usually on the right side. The heart is double,
and a capillary system intervenes between the arteries and veins, but
the liver does not possess a distinct portal system, as in Vertebrates.
(Fig. 102.)
[Illustration: FIG. 102.—Anatomy of Turbo Pica: _p._ Foot. _o._
Operculum. _t._ Proboscis. _ta._ Tentacula. _y._ Eyes. _m._ Mantle
opened longitudinally, to show the disposition of the respiratory
cavity. _f._ Anterior border of the mantle, which, in its natural
position, covers the back of the animal, leaving a wide slit by which
the water enters the branchial cavity. _b._ Gills. _vb._ Branchial vein,
returning to the heart, _c._ _ab._ Branchial artery. _a._ Anus. _i._
Intestine. _e._ Stomach and liver. _ov._ Oviduct. On the upper side of
the neck are seen the cephalic ganglion, and the salivary glands; and at
_d._ is shown a fringed membrane, which forms the lower border of the
left side of the opening that leads to the respiratory cavities. ]
The univalve shell is generally a coiled tube, wound round a central
axis, or _columella_; the nucleus, or earliest part of the shell being
at the apex, and the portion last formed being the open mouth at the
lower part, or base. The direction of the coil may be concentric,
forming a discoidal shell, as _Planorbis_, but it is generally a true
spiral. The mouth, or aperture, of the shell is entire in most
vegetable-feeding Gasteropods, and notched or produced into a canal for
the siphons in the carnivorous species. The former are generally land
and fresh-water forms, and the latter all marine.
Gasteropods comprise three fourths of all living Mollusks, and are
representatives of the type.
Omitting a few rare forms, as _Dentalium_ and _Carinaria_, we may divide
the class into the following orders:
1. _Pteropods_, (Gr., _pteron_, wing; _pous_, foot,) which are small
marine floating Mollusks, whose main organs resemble a pair of fins or
wings, whence the common name, “Sea-butterflies.” Many have a delicate,
transparent shell. The head is said to carry six appendages, armed with
several hundred thousand suckers, forming a prehensile apparatus
unequaled in complication.
[Illustration: FIG. 103.—A. Tritonia Hombergi. B. Horned Doris. ]
2. _Opisthobranchs_, (Gr., _opisthon_, behind; _bragchia_, gills.) These
are generally naked Sea-slugs, a few only having a small shell. The
feathery gills are behind the heart, (whence the name.) They are found
in all seas, generally on rocky coasts. When disturbed, most of them
draw themselves up into a lump of jelly or tough skin. These
naked-gilled Mollusks (_Nudibranchiata_) exhibit a great diversity of
form and a variety of beautiful colors. The Sea-lemon, (_Doris_,) the
beautiful Tritonia, (Fig. 103,) the painted _Eolis_, the Sea-hare,
(_Aplysia_,) which emits a violet or reddish fluid from the mantle when
alarmed, and the Bubble-shell (_Bulla_) are examples.
[Illustration: FIG. 104.—Embryos of Nudibranchiate Gasteropods. ]
The embryo of the naked-gilled Mollusks is very minute, and resembles a
Rotifer rather than a Mollusk. It is inclosed in a transparent
nautilus-like shell, provided with an operculum. (Fig. 104.)
[Illustration: FIG. 105.—Snails and Slugs. ]
3. _Pulmonates_ (having lungs) are air-breathing Gasteropods,
represented by the common Snail. They have the simplest form of lung—a
cavity lined with a delicate net-work of blood-vessels, which opens
externally on the right side of the neck. This opening is covered by a
valve. They are found in all zones, but most where lime and moisture
abound. All feed on vegetable matter. A few are naked, as the Slug; some
are terrestrial; others live in fresh water. The Land-snails, as the
_Helix_, _Bulimus_, and _Limax_, (Slug,) have four horns, the short
front pair being the true tentacles, and the long hinder pair the
telescopic eyes. The Pond-snails, as _Limnæa_ and _Planorbis_, have no
eye-stalks, the eyes being at the base of the tentacles. They are
obliged to come to the surface of the water to breathe. (Fig. 105.)
[Illustration: FIG. 106.—Chiton.]
[Illustration: FIG. 107.—Fissurella Reticulata.]
4. _Prosobranchs._ Having gills in front of the heart. (Gr., _proson_,
before; _bragchia_, a gill.) These are aquatic and generally marine
animals, the most highly organized and most abundant of all the
Gasteropods.
Among the lower forms are the singular _Chiton_, (Fig. 106,) covered
with eight shelly plates; Limpet, (_Patella_,) well known to every
sea-side visitor; and the beautiful Ear-shell Abalone, (_Haliotis_,)
(Fig. 108,) often used for ornamental work and jewelry.
[Illustration: FIG. 108.—Ear-shell, or Haliotis. Reduced.]
[Illustration: FIG. 109.—The Wentle-trap, (_Scalaria_.)]
[Illustration: FIG. 111.—Murex.]
[Illustration: FIG. 110.—Volute Crawling.]
In the higher Prosobranchs the gills are comb-shaped and the sexes are
distinct. The group includes all the spiral univalve sea-shells and a
few fresh-water shells. Many have the aperture entire, as the
fresh-water _Paludina_, the pyramidal _Trochus_, pearly _Turbo_, and
common Periwinkle (_Littorina_) from the sea. Others, the highest of the
race, have the margin of the aperture notched or produced into a canal,
and are carnivorous and marine; such are nearly all the more beautiful
sea-shells, as the Cowry (_Cypræa_) Volute, (Fig. 110,) Olive, Cone,
Harp, Murex, (Fig. 111,) Whelk, (Fig. 112,) and Winged-shell, (Fig.
113.)
[Illustration: FIG. 112.—The Whelk, (_Buccinum_,) showing its
operculum.]
[Illustration: FIG. 113.—Strombus gigas, or “Winged-shell;” one fifth
natural size. West Indies.]
7. CEPHALOPODA, (Gr., _cephale_, head; _pous_, foot.) The class of
Cephalopods stands at the head of the Molluscan type. Some of its forms
surpass in complexity of structure the highest Articulates, although not
so representative of their type as the Gasteropods. They are aquatic
free-swimming or creeping Mollusks, inclosed in a muscular mantle, and
in some species having a univalve shell. The foot is divided into eight
or ten long, waving, but strong tentacles, bearing numerous suckers, or
_acetabula_. The adhesion of these suckers is so great that it is easier
to tear away a limb than to detach it. Their mechanism may be understood
from Fig. 114. The mouth has a horny beak, like a parrot’s bill, but the
jaws do not move vertically, like the bird’s. A long gullet ends in a
muscular gizzard, resembling that of a fowl. Below this is a cavity, the
stomach or duodenum, which receives the bile from a large liver. The
intestine is a tube of uniform size, which, after one or two slight
curves, bends up, and opens into the “funnel” near the mouth. (Fig.
115.) The head is set off from the body by a slight constriction, and is
furnished with a pair of large, staring eyes, which are constructed like
the eyes of Vertebrates, except that there is no aqueous humor, and the
lens, which is double, is bathed freely by the water in which the
animals swim. The nervous system is more concentrated than in other
Invertebrates; the cerebral ganglia are even inclosed in a cartilaginous
cranium. All the five senses are present. The integument contains
pigment sacs, or _chromatophores_, which sometimes tint the animal with
variegated colors. It is probable that they in some way subserve the
sense of sight, as the animal swims with its head backward. Some
Cephalopods have an internal shell, secreted by a fold of the mantle,
called the “cuttle-bone” or “pen.”
[Illustration: FIG. 114.—Suckers on the Tentacles of a Cuttle-fish:
_a._ Hollow axis of the arm, containing nerve and artery. _c._ Cellular
tissue. _d._ Radiating fibers. _h._ Raised margin of the disk around the
aperture _f_, _g_, which contains a retractile membrane, or “piston,”
_i._ ]
[Illustration: FIG. 115.—Morphology of Cephalopoda. Sepia officinalis,
laid open to show viscera, etc. _a._ Foot. _b._ Horny jaws. _c._
Principal ganglion. _d._ Salivary gland. _e._ Œsophagus. _f._ Liver.
_g._ Stomach. _h._ Pyloric cæcum. _i._ Ink bag. _k._ Ovary. _l._
Aperture of atrial system. _m._ Branchiæ. _n._ Oviduct. _o._
Cuttle-bone.]
Two or four pairs of plume-like gills are situated in the pallial
cavity, into which the sea-water is admitted at one end and expelled
through the funnel at the other by muscular contraction. These
contractions serve both for respiration and locomotion, the pressure of
the expelled water driving the animal in an opposite direction. The
systemic heart pumps the blood all over the body, which then returns
through capillaries into veins which conduct the blood back to the
gills, where it is purified, and whence it is propelled to the heart by
contractile sacs, called branchial hearts, placed at the base of each
gill. In addition to other viscera, a large secreting sac, the
_ink-bag_, is often present, containing a dark fluid which the animal
ejects at will through a duct opening at the base of the funnel. The
sexes are always distinct. During reproduction the spermatozoa are
temporarily transferred to one of the arms, which becomes curiously
altered and unfit for locomotion; in this condition it is said to be
_hectocotylized_.
1.) _Tetrabranchs._ This order has four gills, forty or more short
tentacles, and an external chambered shell. The partitions of the shell
are united by a tube, called a siphuncle, and the animal lives in the
last and largest chamber. These chambered shells were once very
abundant. More than two thousand fossil species are known, among which
are the Nautilus, Ammonite, and Orthoceros. They have but one living
representative—the Pearly Nautilus. This straggler of a mighty race
dwells at the bottom of the Indian Ocean. The shell is well known, but
only two or three specimens of the animal have been obtained.
[Illustration: FIG. 116.—The Paper Nautilus, (_Argonauta Argo_.) Fig.
1. Swimming toward the point _a._ 2. Walking on the bottom. 3.
Contracted within its shell, which is partly embraced by the arms. ]
2.) _Dibranchs._ Those having two gills. They are the most active of
Mollusks, and the tyrants of the lower tribes. There are Cuttle-fish and
Poulps (or Devil-fish) so large as even to be dangerous to a man who
might be swimming near them, and the stories of novelists like Victor
Hugo have some foundation in the large size and repulsive aspect of
these creatures. They crawl with their arms on the bottom of the sea,
head downward, and also swim backward or forward, usually with the back
downward, by means of fins, or squirt themselves backward by forcing
water through their funnels.
[Illustration: FIG. 117.—Cuttlefish. ]
The Paper Nautilus (_Argonauta_) (Fig. 116) and the Poulp have eight
arms. The Squid (_Loligo_) and Cuttle-fish (Fig. 117) have ten arms, the
additional pair being longer than the others. Their eyes are movable,
while those of the Argonaut and Poulp are fixed. The Squid, used for
bait by cod-fishermen, has an internal horny “pen,” and the Cuttle has a
spongy, calcareous bone.
CHAPTER XIV.
A R T I C U L A T A .
“Yet wert thou once a worm—a thing that crept
On the bare earth, then wrought a tomb, and slept!
And such is man; soon from his cell of clay
To burst a seraph in the blaze of day!”—ROGERS.
1. THE Articulated type of animals (Lat., _articulus_, a joint) includes
all which possess a distinctly jointed body, as Worms, Crustacea, and
Insects. It contains a greater number and variety of forms than all the
other types put together. The nervous system consists chiefly of a
double chain of ganglia along the ventral surface of the abdomen,
connected together by nerve-filaments. The part representing the brain
is in the form of a ring encircling the gullet. The circulatory
apparatus is a tubular structure running along the back, and
communicating with the body-cavity. The limbs, when present, are jointed
and hollow, and on the same side as the nerve-cords.
There are five classes of Articulates: the aquatic Worms and
Crustaceans, and the air-breathing Spiders, Myriapods, and Insects. It
must be remembered, in accordance with the principles so often referred
to in the present work, that the order of classes in a type is one of
relation rather than of structural rank. Classes cannot be arranged
serially, any more than species, as if one was an improvement on
another, by progressive development. In many respects Myriapods are like
Worms, yet their heads show a resemblance to Insects. Some Spiders are
less complicate than Myriapods, yet for their wonderful instincts Owen
places them above Insects. Insects begin life as worm-like embryos.
Classes in the articulate type depend on the equal or unequal
development of the body-segments, and the number and form of appendages.
Articulates with jointed appendages articulated to the body are called
_Arthropoda_, (Gr., _arthron_, a joint; _podes_, feet.)
2. The class of WORMS, called, also, _Annelida_, or _Annulata_,
(_Annulus_, a little ring,) includes animals with a soft skin and a body
formed of a succession of rings, or movable joints. They differ from the
Arthropoda in not having jointed limbs. A water-vascular system exists,
but it has no connection with locomotion. The blood is often reddish,
but the color does not depend on colored corpuscles, as in vertebrates.
The circulatory apparatus is more highly developed than in Insects.
Some worms can only live as parasites upon the blood or juices of other
animals, and in these the circulatory, water-vascular, and digestive
systems become rudimental, the nervous system is undeveloped, the
body-cavity often vanishes, and the reproductive organs alone are fully
represented.
Order 1. _Tæniada_; (_tænia_, a tape.) Tape-worms, so called from their
length and flatness. They live chiefly in the digestive canal of higher
animals. Three species are occasionally parasitic in man. The head,
which is the true animal, is provided with hooks or suckers, by which it
adheres to the mucous membrane of its host. It feeds by imbibition,
(_osmosis_,) there being no mouth or alimentary canal. The joints, or
segments, are called _proglottides_, (singular, _proglottis_,) and are
but successive growths containing ova. The life-history of these worms
is a curious instance of alternation of generations. The fertilized ova
are set free by the decomposition of the joint, or proglottis. They are
then swallowed by some animal, and the tough capsule is dissolved,
setting free the embryo, which travels through the tissues of its host
as a little oval body, bearing weak, hook-like, or boring spines. On
reaching a suitable site, as the liver, it anchors, and the body dilates
into a cyst, or sac full of water, (_Cysticercus_.) Many animals,
formerly known as cystic worms, have been found to be but transitional
stages of Tæniæ. In this condition the animal may remain a long while
and generate new cysts by budding, but when the flesh containing the
“scolex,” or resting-larva, is eaten by some other animal, the outer
wall of the cyst dissolves, and becomes a true Tape-worm. The human
Tape-worm has its cystic stage in “measly” pork, while the Tape-worm of
the dog develops from cysts found in the hare, and that of the cat from
cysts in the mouse; most cases requiring two animals as hosts for
perfecting the growth of the worm. (Fig. 118.)
[Illustration: FIG. 118.—Morphology of Tæniada. _a._ Ovum with
contained embryo. _b._ Cysticercus longicollis. _c._ Head of Tænia
solium, (enlarged;) the circlet of hooklets is at the top, and below
them are those of the cephalic suckers. _d._ A single segment or
proglottis magnified. 1. Generating pore. 2. Water vessels. 3. Dendritic
ovary. _e._ Portion of Tape-worm, natural size, showing the alternating
arrangement of the generative pores. ]
Order 2. _Trematoda_; the Flukes. (Gr., _trema_, a hole.) These are flat
or roundish parasitic worms. The intestine is branched, and, as in
Cœlenterata, there is but a single opening, which serves for both mouth
and anus. There are suckers at the anterior end of the disk. They are
met with sometimes in the liver of the sheep.
[Illustration: FIG. 119.—Structure of Polycelis levigatus, (Planarian
worm.) ]
Order 3. _Turbellaria._ These are non-parasitic, and may be found on the
sea-shore, under stones, or in fresh-water pools, or on moist ground.
They are small, ciliated, and flat worms, which glide with a slug-like
motion over wet surfaces, or swim by the vibrations of their cilia. In
the small flat _Planarians_ the digestive cavity is greatly branched.
(Fig. 119.) In others it is a simple pouch, with no excretory orifice.
In the larger forms it is elongated. Some of the largest (the
_Nemerteans_) are like long ribbons; sometimes, as in _Borlasia_, being
twelve feet long.
Order 4. _Acanthocephala_; (_akantha_, a thorn; _cephale_, head,) are
rounded, parasitic worms, having a protrusible proboscis, armed with
recurved hooks. Their structure is not unfrequently as simple as the
Protozoa, having no alimentary canal whatever, and subsisting by
absorption. Like the Tape-worms, they develop through an alternation of
generations.
Order 5. _Gordiaceæ._ The horse-hair-like worm found in rain pools is an
example of this order. It begins life as a little larva in mud or water
pools. By means of its boring spines it pierces the body of a
grasshopper, beetle, or other insect, where it becomes encysted, and
grows often ten times as long as its host, when it becomes free and
aquatic, and produces its eggs. Some of these, as the _Mermis albicans_,
multiply so rapidly as to give rise to a popular belief that they fall
as “worm-rains." They have remarkable tenacity of life, as they can be
dried into brittle threads, and yet become active on being moistened.
Order 6. _Nematoidea_, (_nema_, thread; _eidos_, form.) Thread-worms, or
round worms. These are both free and parasitic. Some of them, as the
_Ascaris lumbricoides_, or common round worm, often infests the small
intestines of children, while the _Trichina spiralis_, a minute worm
found encysted in the flesh of swine, when introduced into the human
body, multiplies so rapidly in the muscles as to give rise to dangerous,
and even fatal symptoms. The “eels” in vinegar and sour paste also
belong to this order.
[Illustration: FIG. 120.—Rotifer vulgaris.]
Order 7. _Rotifera_, or _Wheel Animalcules_. These are microscopic in
size, but so transparent that the details of organization can easily be
seen. The male rotifers are few and small, and have no digestive canal,
but the females have a complete nutritive system, and many species are
provided with an organ for mastication resembling an anvil acted on by
two hammers, another instance of peculiarity of structure for a special
end. These animals are capable of reviving on being moistened, after
having been dried up, and that many times in succession. (Fig. 120.)
Order 8. _Gephyrea_, (_gephura_, a bridge,) so called in allusion to the
apparent connection which they exhibit between Echinoderms and
Articulates. They are sometimes called Spoon-worms, Squirt-worms, and
Siphon-worms, (_Sipunculus_.) They have all the aspect of worms, but the
circle of tentacles round the mouth show their affinity to Holothurians.
They live in the sand, or seek protection in some empty univalve shell.
Their elongated bodies contain a long, tortuous intestine, ciliated
inside and outside. They have no locomotive processes, nor are there
calcareous or silicious spicules in their skin. The mouth has a long
proboscis.
Order 9. _Suctoria_, or Leeches. These are aquatic worms, with a soft,
segmented body, provided with a suctorial disk at one or both ends. The
mouth of the common Leech (_Hirudo medicinalis_) is armed with three
horny, semi-lunar plates, with finely serrated teeth, which act as saws,
enabling the leech to make incisions in the skin of its host through
which to suck the blood.
[Illustration: FIG. 121.—Lob-worm, (_Arenicola piscatorum_,) a
dorsibranchiate, showing the tufts of capillaries, or the external ills.
The large head is without eyes or jaws. ]
[Illustration: FIG. 122.—Serpula.]
Order 10. _Chœtopoda_, or _Bristle-footed_ worms. Some of these occur
under the stones of the sea-shore, as the lug-bait of fishermen. (Fig.
121.) Others secrete a glutinous material from the surface, which
cements sand and other foreign bodies into a tube. Others secrete
calcareous matter, which forms a tubular residence, as the common
_Serpula_, whose white, snake-like concretions abound on the stones and
shells of the shore, and the _Spirorbis_, whose minute whorled shells
dot the surface of many sea-weeds. Some of the _Nereids_, or
Sea-centipedes, attain to a considerable size, one species being four
feet long. The Sea-mouse (_Aphrodite_) also belongs to this order. The
latter is clad with iridescent scales and bristles, or barbed spines.
Those who bear the gills along the back have been called
_Dorsibranchiates_. These gills are found close to the root of the
dorsal oar, or bristle, and the blood is purified by being exposed to
the oxygen held in solution in the sea-water. Those worms which live in
tubes (_Tubicolæ_) have the gills developed only on the foremost
segments of the body, and the dorsal and ventral oars of the other
joints are rudimentary, but they have branching tentacle-like processes
about the head. In _Serpula_ one of the tentacles is formed into a lid,
or operculum, with which the open mouth of the tube can be closed at
will. (Fig. 122.)
The common Earth-worm (_Lumbricus_) has few and small bristles, in the
form of recurved hooks on each ring of the body, which assist in
locomotion. It possesses no external gills, but respires by internal
ciliated processes. The nervous system is often but little developed.
The mouth is on the second segment, and the digestive canal is a
straight tube, which is wide, and always full of earth, which these
animals devour for the sake of the organic particles contained in it;
the remaining part being cast out and heaped at the outlet of their
burrows, as “worm-casts.” For better division of the material swallowed
the digestive canal has a muscular gizzard about fifteen rings from the
mouth. They are propagated by eggs.
[Illustration: FIG. 123.—Circulating Apparatus of Lobster: _a._ Heart.
_b._ _c._ Arteries to the eyes and antennæ. _d._ Hepatic artery. _e._
_f._ Arteries to thorax and abdomen. _gg._ Venous sinus. _h._ Gills.
_i._ Branchial veins. ]
3. The class of CRUSTACEA, (_crusta_, a crust or shell,) includes all
Articulates with jointed legs and gills. They have a double, or complete
circulation of blood; a dorsal tube, or heart, sending off a system of
arteries, not found in insects; but the blood, as it leaves these tubes,
escapes into the general cavity, as in other Articulates. (Fig. 123.)
The shell, or _carapace_, has for its base a horny substance called
_Chitine_. It is also found in the covering of Insects. In the Crab and
Lobster there is a large proportion of carbonate of lime combined with
this, rendering the carapace extremely hard. In others, a mixture of
chitine and albumen gives rise to a softer integument. The rings of the
body have considerable freedom of motion, by means of striated or
voluntary muscles. The normal number of joints is twenty-one, but two or
three are often blended. To each of these joints, except the last, there
is attached a pair of members, the forms and uses of which vary in
different species, and at different ages. These members are jointed, and
covered with a similar envelope, or crust, to that of the body. As the
body grows the carapace does not grow in the same proportion, rendering
frequent moltings necessary. The entire covering is thrown off from
body, feet, and antennæ in the most perfect manner. The Crustacea differ
in habits as well as in structure. Most live in the water, but the
_Land-crabs_ inhabit the land. The Hermit-crabs (_Paguridæ_) live in the
empty shells of Mollusks, which they seize, often killing the
inhabitant. The majority of Crustaceans have jaws and organs of
mastication, but some have no such organs, but live as parasites,
especially on fishes, sucking their juices, and becoming strangely
deteriorated. The alimentary canal in this class consists of a short
gullet, a gizzard-like stomach, and a straight intestine. Crustaceans
pass through a series of strange metamorphoses before reaching their
adult form. The _Balanus_, or acorn-shell, which incrusts the rocks of
the sea-coast in great numbers, begins life as an active, one-eyed free
swimmer, called a “_Nauplius_” which after one or two molts becomes a
pupa, inclosed in a bivalve shell by a folding of the dorsal portion.
Finally it becomes a sedentary Cirripede, (_cirrus_, a curl; _pes_, a
foot.) (Fig. 124.) It will be convenient to divide Crustaceans into four
groups, or orders.
[Illustration: FIG. 124.—Development of Balanus balanoides: A. Earliest
form. B. Larva after second molt. C. Side view of the same. D. Stage
immediately preceding the loss of activity. _a._ Stomach.(?) _b._
Nucleus of future attachment.(?) ]
1.) _Cirripeds_, distinguished by being fixed, having a shelly covering,
and by their feathery arms. Such are Barnacles, (_Lepas_,) which have a
peduncle, or stalk, and are often found on the backs of whales or on
ship’s bottoms, and Acorn-shells, (_Balanus_,) which are sessile.
[Illustration: FIG. 125.—Water-fleas: 1. Cyclops communis. 2. Cypris
unifasciata. 3. Daphnia pulex. ]
2.) _Entomostracans_, which have a horny shell and no abdominal limbs;
represented by the little Water-fleas, (_Cyclops_,) (Fig. 125,) of our
ponds, the King-crabs (_Limulus_) and the extinct Trilobites. The
abdomen of the King-crab is reduced to a mere spine, the appendages
about the mouth are used for locomotion, and their eyes are smooth.
3.) _Tetradecapods_, small fourteen-footed species; as the Wood-louse,
or Sow-bug, (_Oniscus_,) found in damp places, and the Sand-flea,
(_Gammarus_,) seen in summer on the sea-shore.
[Illustration: FIG. 126.—Metamorphosis of Crustacea, (_Carcinus
mænas_.) _a._ Larval or first form. _b._ Second stage. _c._ Third stage.
_d._ Final stage, in which the metamorphosis is complete. ]
4.) _Decapods_, having ten legs, as the Shrimp, (_Crangon_,) Cray-fish,
Lobster, (_Astacus_,) and Crab, (_Cancer_.) Crabs differ from Lobsters
chiefly in being formed for creeping at the bottom of the sea instead of
for swimming, and in the abdomen, or tail, being a mere rudiment which
folds into a groove under the enormous thorax. The curious metamorphosis
of the Crabs is illustrated in Fig. 126. At first the embryo is a
comical-looking animal, with a sort of spiked helmet on its head. It has
two large eyes and a well-developed abdomen. It is called a “Zoea,” and
was formerly described as a distinct genus. After a succession of molts
it becomes a perfect Crab.
4. ARACHNIDA (_arachne_, a spider) is a class much resembling the
Crustaceans, having the body divided into a cephalo-thorax and abdomen.
The head carries two, six, or eight eyes, which are not compound bundles
of crystal rods covered by a common cornea, as in Crustaceans, but
separate transparent cones surrounded with pigment. Antennæ are only
two, if present, and are not used as “feelers,” but serve prehension of
food. Mandibles are always present, and in Scorpions the maxillary palps
form pincers, or claws, like those of a Crab. Such claws are called
_chelæ_, (_chele_, a claw.) Arachnids are all air-breathers, having
spiracles which open into air-sacs, or tracheæ. The young of the higher
forms undergo no metamorphosis after leaving the egg. The class is
divided into three orders: Mites, Scorpions, and Spiders.
1.) _Mites_ are the simplest forms of the class. They have no marked
articulations, the head, body, and thorax being in one piece. They have
no brain, but a single ganglion in the abdomen. They breathe by tracheæ.
The mouth is formed for suction. Most are parasitic on animals or
plants. Mites (_Acarus_) include the Cheese-mite, the Itch-insect, and
many similar forms. The Ticks (_Ixodes_) have a piercing beak and a
leathery skin.
[Illustration: FIG. 127.—Scorpion.]
2.) _Pedipalpi_, or Scorpions, have maxillary palpi ending in forceps,
and a prolonged jointed abdomen. (Fig. 127.) Breathing takes place by
pulmonary sacs, similar to spiders. The nervous and circulatory systems
are highly organized. The last joint of the abdomen bears in scorpions a
sharp spine at its end, perforated by the duct of a poison-gland,
whereby it inflicts painful wounds. The _Chelifer_, or Book-scorpion,
sometimes found in old books, has no sting. The _Phalangers_, or
Harvest-spiders, with long hooked palpi and long ungainly legs, belong
to this order.
3.) _Araneida_, or Spiders, have the cephalo-thorax joined to the
sac-like abdomen by a narrow constriction, and are provided at the
posterior end with two or three pairs of appendages called “spinnerets.”
The use of the spinnerets is to reel out the silk for their web from the
silk-glands. The tip of each is perforated by many pores, through which
the silk escapes, so that each thread of the web may consist of several
hundred strands. The silk is fluid at first, but rapidly hardens. The
hind feet have comb-like claws for pressing the silk together. Sometimes
one pair of the hinder appendages consists of palpiform organs. The
mandibles are vertical, and end in a powerful hook. The maxillæ, or
palpi, which in Scorpions are powerful claws, in Spiders resemble
thoracic feet. The brain is of large size, and the nervous system
greatly concentrated.
The instincts of Spiders are very remarkable. They are the most wily of
Articulates. They display great skill and industry in weaving their
webs, and some species (called Mason-spiders) excavate cavities in the
ground, which they line with a silken web, and close the entrance with a
lid which moves upon a hinge.
5. MYRIAPODA (_myrios_, numerous; _pous_, foot) is a small class,
including the Centipedes and the Millipedes. The body is divided into
segments, twenty or more, to each of which legs are appended. They
resemble Worms in their form, and in the simplicity of their nervous and
circulatory systems; but the skin is hardened by chitine and the legs
are articulate. They breathe by trachea, or tubes, have two antennæ, and
a variable number of eyes.
1.) _Chilognatha_, (_cheilos_, lip; _gnathos_, jaw.) This order contains
the Thousand-legged Worm, (_Julus_.) The body is round, legs very
numerous, sometimes a hundred pairs, each segment having two pairs.
Mouth without palpi. Lower lip composed of confluent maxillæ. They are
of slow locomotion, harmless, and vegetarian.
2.) _Chilopoda_, (_cheilos_, lip; _pous_, foot,) are characterized by a
flat body, with fifteen to twenty pairs of legs. The mouth possesses a
hollow duct for the passage of fluid from a poison-gland. The terminal
section of the body carries a pair of spines. Sometimes the tail is
curved into a formidable poisonous hook, as in the Scorpion. In
temperate climates the Chilopoda are harmless, but often dangerous in
hot countries. Such is the Centipede, (_Scolopendra_.)
6. INSECTA. This class contains more species than all the rest of the
Animal Kingdom, 150,000 having been already described. Its typical
character is well marked, yet it contains a large number of instances of
special structure, arranged for evident purpose. Chap. III, Sec. 9, and
Chap. V, Sec. 6.
[Illustration: FIG. 128.—Diagram of Insect, (_Blatta orientalis_.) _a._
Head with compound eyes and antennæ. _b._ Prothorax with first pair of
legs. _c._ Mesothorax with second pair of legs and first pair of wings.
_d._ Metathorax with third pair of legs and second pair of wings. _e._
Abdomen without limbs, but carrying terminal appendages, which are
subservient in reproduction. ]
The body is divided into three principal segments—a head, a threefold
thorax, and a ringed abdomen. (Fig. 128.)
The head contains the organs of sense, and supports two antennæ, which
are supposed to be organs of touch and of hearing, as well as of
communication between one insect and another. There are many forms of
antennæ, but all are tubular and jointed. The eyes are usually compound,
although there are also sometimes a cluster of simple eyes, or _ocelli_.
The compound eyes have a transparent surface, or cornea, divided into
many facets, each of the nerve-rods having its own pigment mass and its
own cornea. (Fig. 129.) The common house-fly has two thousand such
facets in each eye, and in the dragon-fly there are twenty-eight
thousand.
[Illustration: FIG. 129.—Head and Eyes of the Bee. _a._ _a._ Antennæ.
_b._ Ocelli. A. Facets enlarged. B. The same with hairs growing between
them. ]
The thorax consists of three pieces, the _prothorax_, _mesothorax_, and
_metathorax_, each having a pair of legs; the wings, when present, arise
from the last two segments.
The abdomen contains the viscera and the organs of reproduction. Legs
are never attached to it.
The “brain,” as it is called, is a mass of ganglia lying across the
upper side of the throat behind the mouth, and the principal nerve cord,
with a ganglion for each segment, runs along the ventral side of the
body.
[Illustration: FIG. 130—Circulation in insects. The arrows indicate the
course of the blood.]
[Illustration: FIG. 131.—Digestive Apparatus of Beetle. _a._ Pharynx.
_b._ Œsophagus. _c._ Crop. _d._ Gizzard. _e._ Chylific stomach. _f._
Small intestine. _g._ Rectum. _h._ Biliary vessels. ]
The digestive apparatus consists of pharynx, gullet, (sometimes a crop,)
gizzard, stomach, and intestine. The liver is represented by tubes
opening into the intestine. Many insects have glandular tubes, called
from their first describer, Malpighian, which open at the end of the
intestine. (Fig. 131.) Some have also salivary glandular tubes and silk
organs. Insects have no absorbent vessels, the chyme transuding through
the walls of the canal. The blood, usually colorless, is propelled by a
pulsating tube divided into valvular sacs, which allow the current to
flow only toward the head. (Fig. 130.) From this tube it escapes into
the cavities of the body.
[Illustration: FIG. 132.—Respiratory Apparatus of Insect, (_Nepa_.)]
Respiration is provided for by a tracheal system; the air circulating in
vessels instead of the blood, as in other classes. A row of apertures
(_spiracles_) on each side of the body, often provided with a net-work
of fibers to keep out foreign substances, communicate with branching
tubes, whose membraneous wall is strengthened and kept open by a coiled
spinal filament. (Fig. 132.) What are called the “nerves” of an Insect’s
wing are double tubes, the inner one being a tracheal branch supplying
air, and the outer one, sheathing it, is a blood-vessel.
[Illustration: FIG. 133.—Masticatory mouth of Insect. _a._ Labrum, or
upper lip. _b._ Labium, or lower lip, with jointed palpi. _c._ Maxillæ,
with jointed palpi. _d._ Mandibles. ]
The mouth of an Insect is a very complicate apparatus. Some are
_Masticatory_, or fitted for biting, as in Beetles. (Fig. 133.) Others
are _Suctorial_, or for sucking, as in Butterflies. These last form a
long double tube, or spiral trunk, (_proboscis_,) serving to pump up the
juices of flowers. The masticating mouths consist of two pairs of horny
jaws, (_mandibles_ and _maxillæ_,) which work horizontally between an
upper (_labrum_) lip and an under (_labium_) lip. The maxillæ and under
lip carry sensitive jointed feelers, (_palpi_.) The front edge of the
labium is generally known as the tongue, (_ligula_.)
[Illustration: FIG. 134.—Head of a Bee.]
In the Bee tribe, instead of maxillae, we find a sheath inclosing a
long, slender, hairy tongue. Entomologists have retained the same names
to the different parts, under the influence of the theory of
transmutation. (Fig. 134.)
[Illustration: FIG. 135.—Proboscis of a Dipterous Insect, (_Tabanus_.)]
The proboscis of the Fly is an enlarged lower lip, (Fig. 135;) that of
the Bugs is formed by four bristles, fitted both for piercing and
sucking.
Most Insects undergo metamorphosis, and exhibit four states of
existence: egg, larva, pupa, and imago. The larva has little resemblance
to its parent, eating and growing rapidly. It wraps itself in a cocoon
and enters the pupa state, remaining apparently dead till new organs
are developed, when it emerges a perfect winged Insect, or imago.
[Illustration: FIG. 136.—A. Larva of Mosquito. B. Escape of Mosquito
from its Pupa-case.]
Insects have six legs, each having five parts; the _coxa_ or hip, the
_trochanter_, the _tibia_ or shank, and the _tarsus_. The last is
subdivided into joints, generally five, and a pair of claws. Such as can
walk on glass, or upside down, as the Fly, have two or three disks
(_pulvilli_) between the claws. It used to be supposed that these disks
acted as suckers, but it is now believed that each hair is a minute tube
containing a viscid fluid by which the Fly adheres.
[Illustration: FIG. 137.—A. Foot of _Dytiscus_, showing its apparatus
of suckers. _a._ _b._ Large suckers. _c._ Ordinary suckers. B. One of
the ordinary suckers more highly magnified. ]
The male of the Great Water-beetle (_Dytiscus marginalis_) has a
peculiar apparatus of suckers, large and small, on his front legs, which
may be useful, but, judging from their beautiful fringes as seen under
the microscope, appear rather ornamental. (Fig. 137.)
Order 1. _Neuroptera_; (_neuron_, nerve; _pteron_, wing,) includes
Dragon flies, (_Libellulidæ_,) (Fig. 138;) Caddis flies,
(_Plioganeidæ_,) May flies, (_Ephemeridæ_,) the Ant-lion, (_Mygonalis_,)
and the Termite Ants. The mouth is masticatory; wings four, equal in
size, membraneous and lace-like.
[Illustration: FIG. 138.—1. Dragon-fly, (_Libellulina depressa_.) 2.
Grasshopper, (_Gryllus_.) 3. Bee, (_Apis mellifica_.) 4. Fly, (_Musca
domestica_.) 5. Butterfly, (_Pontia brassicæ_.) 6. Musk-beetle,
(_Cerambyx moschatus_.) ]
Order 2. _Orthoptera_; (_orthos_, straight; _pteron_, wing,) embraces
the Crickets, (_Achetina_,) Grasshoppers, (_Gryllina_,) (Fig. 138,)
Locusts, (_Locustina_,) and Cockroaches, (_Blattina_.) Mouth
masticatory. Wings four, or wanting; anterior pair small, thickened, and
overlapping along the back; the hinder pair broad, net-veined, and
folding like a fan. Legs various, being powerful jumping organs in
grasshoppers, _raptorial_ (_raptor_, a plunderer) in Mantis; _cursorial_
(_curro_, to run) in Locusts. Each family produces sounds which are
characteristic, and which are supposed to be produced by the rapid
friction of the long hind legs against the wing. The sound of the
Grasshopper is said to be the highest known musical note.
Order 3. _Hemiptera_, (_hemi_, half; _pteron_, wing,) have a suctorial
mouth, produced into a long, hard beak. The four wings are irregular and
sparsely veined, or wanting. The body is flat above, and the legs
slender. In some the four wings are opaque at the base, and transparent
at the apex, whence the name of the order. Some feed on the juices of
animals, and some on plants. Plant-lice, (_Aphides_,) the wingless
Bed-bug, (_Cimex_,) and Louse, (_Pediculus_,) the Squash-bug,
(_Coreus_,) Water-boatman, (_Notonecta_,) Seventeen-year Locust,
(_Cicada_,) and the Cochineal, (_Coccus_,) are examples.
Order 4. _Coleoptera._ (_Koleos_, a sheath; _pteron_, wing.) This is the
largest of the orders, containing about ninety thousand species. The
thickened, horny fore-wings, or _elytra_, (_elytron_, a sheath,) are not
used for flight, but to cover the hind pair. When at rest the elytra are
united by a straight edge along their length, and the hind wings are
folded transversely. The mouth is armed with formidable mandibles; the
integument is generally hard, and the legs are strong. The larvæ are
worm-like, and the pupa is motionless. The highest tribes are
carnivorous. Among them we find the Tiger-beetles, (_Cicindela_,) the
common Ground-beetles, (_Carabus_,) whose hind wings are often absent,
the Diving-beetles, (_Dytiscus_,) with boat-like body and oar-like hind
legs, the Carrion-beetles, (_Silpha_,) with black, flat bodies and
club-shaped antennæ, the Goliath-beetles, (_Scarabæus_,) the
Snapping-bugs, (_Elata_,) the Lightning-bugs, (_Pyrophorus_,) the
spotted Lady-birds, (_Coccinella_,) the Long-horned beetles,
(_Cerambycidæ_,) and the destructive Weevils, (_Curculionidæ_,) with
pointed snouts. (Fig. 138.)
Order 5. _Diptera_, or two-winged Flies; have the hinder pair of wings
replaced by “poisers,” or “_halteres_.” A few species are wingless. The
eyes are large, with many facets; the tongue terminates in a fleshy
knob, and the rest of the mouth is suctorial, and furnished with fine
lancets; the thorax is globular, and the legs slender. The larvae are
footless grubs. Among them are House-flies, (_Muscæ_,) (Fig. 138,)
Gnats, (_Culicidæ_,) Crane-flies, (_Tipulidæ_,) Forest-flies,
(_Hippoboscæ_,) and Gad-flies, (_Gabrinidæ_.) The wingless Flea
(_Pulex_) is also placed in this order.
Order 6. _Lepidoptera_, (_lepis_, scale; _pteron_, wing,) includes
Butterflies and Moths. They have four large wings, thickly covered on
both sides with minute overlapping scales, of different colors, and
often arranged in patterns of exquisite beauty. These scales are
epidermic appendages of a similar nature to hairs, and every family has
a special form of scale. The head is small, the body is cylindrical, and
the legs are little fitted for locomotion. The mouth is a proboscis, or
coiled tube, sometimes an inch long. The caterpillar, or larva, has a
worm-like form, and from one to five pairs of abdominal legs, in
addition to the six on the thorax. The mouth is formed for mastication.
There are three groups: the gay Butterflies, (Fig. 138,) having knobbed
or hooked antennæ, flying in the sunshine only, and keeping their wings
vertical when at rest; the dull-colored Sphynges, or evening Moths, with
antennæ thickened at the middle, and flying at twilight; and the
nocturnal Moths, whose antennæ are thread-like and often feathery, and
which prefer the night. The pupa of Butterflies is unprotected, and is
generally suspended by a silken thread. The pupa-case is generally
ornamented with golden spots, hence the common name, _chrysalis_. The
pupa of Moths is inclosed in cocoons.
Order 7. _Hymenoptera_, (_hymen_, membrane; _pteron_, wing,) includes
Bees, (Fig. 138,) Wasps, Ichneumons, Saw-flies, and Ants. The mouth is
fitted for both biting and suction; the legs are for locomotion as well
as support; and the four membraneous wings are equally transparent, and
interlock by small hooks during flight. The females are usually provided
with a sting, or borer. The larvæ are footless, helpless grubs,
generally nurtured in cells, or nests.
The colony of Bees is formed of the perfect female, called the
“Queen-bee,” many perfect males, or drones, and a swarm of sexless bees,
the neuters, or workers. The drones and the neuters are produced by
parthenogenesis. (Chap. III, Sec. 16.)
The “vespiary” of the Wasps, like the hive of the Honey-bee, contains
males, females, and neuters; but the perfect males work equally with the
neuters.
Ants (_Formicidæ_) also form colonies, and the observations made upon
many species show a wonderful amount of intelligence in these creatures.
In many ant-colonies the neuters consist of two classes—“the workers,”
who do all the building and storing of the little town, and “the
soldiers,” who defend the works. Their treatment of Plant-lice, or
Aphides—keeping them, and milking them as men do cows—their
slave-capturing expeditions, and the recently-discovered agricultural
ant-colonies, furnish abundant food for the propensity to the marvelous
in human nature, and prove to the philosophic observer of creation how
closely related are all living things to properties of thought,
affection, and will, which are generally regarded as spiritual rather
than material.
CHAPTER XV.
V E R T E B R A T A .
Thus the seer,
With vision clear,
Sees forms appear and disappear,
In the perpetual round of strange
Mysterious change
From birth to death, from death to birth,
From earth to heaven, from heaven to earth;
Till glimpses more sublime
Of things unseen before,
Unto his wondering eyes reveal
The Universe, as an immeasurable wheel
Turning for evermore
In the rapid and rushing river of Time.
—LONGFELLOW.
1. The type, or sub-kingdom, Vertebrata, (_vertebra_, a joint of the
back, from _vertere_, to turn,) is characterized by the separation of
the greater part of the nervous system from the general cavity of the
body. A transverse section of the body exhibits two cavities, or tubes;
the dorsal, or neural, tube, containing the cerebro-spinal nervous
system, and the ventral, or hæmal tube, inclosing the alimentary canal,
heart, lungs, and a double chain of ganglia belonging to the sympathetic
system of nerves. The ventral cavity, with its contents, corresponds to
the whole body of an Invertebrate animal, while the dorsal tube is
distinctly typical.[24]
Vertebrates have an internal, jointed skeleton, capable of growth and
repair. (Chap. IV, Sec. 13, _d_.) During embryonic life it is
represented by the _notochord_, a fibro-cellular rod, tapering to either
end, but this is replaced by a more highly developed column of cartilage
or bone, except in the doubtful _Amphioxus_. The column and cranium are
never absent, although other parts may be wanting, as the ribs in Frogs,
limbs in Snakes, etc. The limbs never exceed four, and when present, are
always articulated to the internal skeleton, on the ventral side of the
body, while the limbs of Invertebrates are developed from an external
skeleton, on the neural side. The muscles moving the limbs are attached
to the endoskeleton and not to the exoskeleton, as in Invertebrates.
Muscular tissue is found in all animals, from Radiates to Man. The most
complete development of muscles is in the _Pentacrinus_. (Chap. XII,
Sec. 5.) Voluntary muscular tissue always has a transversely striated
appearance under the microscope, (Fig. 139,) while those fibers not
under the control of the will are smooth.
[Illustration: FIG. 139.—Muscular Fibers. Magnified 200 diameters.]
[Illustration: FIG. 140.—Plan of Circulation in Fishes: _a._ Auricle.
_b._ Ventricle. _c._ Pulmonary Artery. _e._ Pulmonary Veins, bringing
blood from the gills, _d_, and uniting in the Aorta, _f._ _g._ Vena
Cava. ]
The circulation of the blood is complete in Vertebrates, the arteries
being joined to the veins by capillaries, so that the blood never
escapes into the visceral cavity, as in the Invertebrates. All have a
portal vein, carrying blood through the liver, and all have lacteals and
lymphatics. The blood is red, and contains both red and white
corpuscles. The teeth are developed from the dermis, never from the
cuticle, as in Mollusks and Articulates; the jaws move vertically, and
are never modified limbs. The liver and kidneys are always present. The
respiratory organs are either gills or lungs, or both. Vertebrates are
the only animals which breathe through the mouth.
The arrangement of the circulatory system varies in the different
classes, in accordance with the structure of the respiratory organs. In
Fishes (Fig. 140) the heart is double as in the Oyster, but instead of
driving arterial blood over the body, it receives the returning, or
venous blood, and sends it to the gills. From the capillaries of the
gills the blood is passed into a large artery, or _aorta_, along the
back, which distributes it by a complex net-work of capillaries among
the tissues. These capillaries unite with the ends of the veins which
pass the blood into the auricle of the heart, after purification in the
liver and kidneys.
In Amphibia and Reptiles (Fig. 141) the heart has three cavities: two
auricles and one ventricle. The venous blood from the body is received
into the right auricle and the purified blood from the lungs into the
left. Both communicate with the ventricle, which pumps the mixed blood
part to the lungs and part around the system.
[Illustration: FIG. 141.—A. Plan of Circulation in Amphibia and
Reptiles. B. Plan of Circulation in Birds and Mammals. _a._ Right
Auricle receiving venous blood from the system. _b._ Left Auricle
receiving arterial blood from the lungs. _c._ _c._ Ventricles. _d._ _e._
_f._ Systemic Artery, Vein, and Capillaries. _g._ _h._ _k._ Pulmonary
Artery, Vein, and Capillaries. ]
The highest form of circulation is seen in the warm-blooded Vertebrates,
Birds, and Mammals. The heart has four cavities—a right and left
auricle, and a right and left ventricle. The right auricle receives the
blood from the veins, transmits it to the right ventricle, which sends
it to the lungs. The left auricle receives it from the lungs, and sends
it to the left ventricle, which propels it over the body. The two
auricles contract together, and so also do the ventricles, making
certain faint sounds, which may be imitated by the words _lubb tup_.
(Fig. 141.)
The greatest differences between Vertebrates and other animals are found
in the Nervous system, which, as we have seen, has a distinct tube or
cavity in this type, altogether unlike the plan of structure elsewhere.
In living things, like the Protozoa, or Protophytes, which are composed
of a simple mass of bioplasm, all the functions necessary for animal or
vegetable life belong equally to every atom of the mass. In Chap. V,
Sec. 7, it was shown that the simplest plants and animals differ from
the highest, or more complex, only in the modification of some parts of
the structure to serve special functions. Thus locomotion is served by
the change of bioplasm into muscle, or bone, external protection by
transformed epidermal bioplasm, as described in Chap. IV. To regulate
and harmonize the complex organs of digestion, respiration, circulation,
and secretion, and to conduct sensation and motor force, seems to have
been the object of the change of bioplasm into nervous matter.
Nerve matter exists in the form of cells and of fibers. The cells are
soft and grayish, and are generally found accumulated in masses or
_ganglia_, sometimes called nerve-centers. The fibers are of two kinds,
one soft and nucleated, the ganglionic or sympathetic fibers, and
ordinary nerve-fibers.
These latter are for a great part of their length inclosed in a
transparent sheath, which coagulates after death into a white
substance—the white substance of Schwann. A number of these fibers,
thus ensheathed, are bound in bundles, which are called _nerves_. Some
of these fibers proceed or conduct impressions from the surface, or from
the different organs where they are found, toward the gray centers only,
and are called _afferent_ or sensory nerves. Others conduct an influence
from the centers to contract or move the muscles, and are called
_efferent_, or motor nerves. Thus, on receiving any impression, as the
prick of a pin, an afferent nerve conducts the impression to the center,
from which an efferent nerve conducts power for the muscles to contract.
If the afferent nerve of a part is cut across or injured, sensation is
lost, but motion remains; but if the efferent nerve is cut, the power of
motion is lost while sensibility continues. This form of nerve-action is
called _reflex_. Many actions of this sort are wholly involuntary, as
the motions of the limbs in paralytics excited by tickling the soles of
the feet.
In the Star-fish we find a nervous ring around the mouth, made of five
ganglia, with radiating nerves, corresponding with the type of
structure. The Mollusks have an irregularly scattered nervous system,
consisting of two or more ganglia around the gullet and one or two more
in the posterior region, united by threads, and sending fibers to
various organs. The Articulates have generally a double nervous cord
along the ventral side, studded with ganglia of nearly uniform size,
except the first, which is largest. In the higher forms, as the Bee,
several ganglia are fused together in the head and thorax, indicating a
concentration of organs for sensation and locomotion.
The nervous system of the Invertebrates is _homologically_ represented
by the ganglionic or sympathetic system of Vertebrates, which supplies
the unstriped or involuntary muscles, and presides over organic or
visceral functions, such as digestion and circulation. In addition to
the sympathetic system, Vertebrates have a brain and spinal cord,
forming the cerebro-spinal system, (Fig. 142,) to which there is nothing
similar in other animals, and which presides over what are called the
functions of animal or sentient life, as sensation and locomotion. Yet
as many Invertebrates exhibit sensibility and voluntary actions, it
follows that _analogically_ the nervous system in them represents both
the sympathetic and cerebro-spinal systems of Vertebrates.
[Illustration: FIG. 142.—Human Brain and Spinal Cord, one fifth natural
size. _a._ Great longitudinal fissure. _b._ Anterior lobe. _c._ Middle
lobe. _d._ Medulla oblongata. _e._ Cerebellum. _f._ First spinal nerve.
_g._ Brachial plexus of nerves supplying the arms. _h._ Dorsal nerves.
_i._ Lumbar nerves. _k._ Sacral plexus of nerves for the limbs. _l._
Cauda equina. The figures indicate the twelve pairs of cranial nerves of
which one is olfactory, two are optic, and eight auditory. ]
The form of the brain differs much among Vertebrates. In some the
cerebral hemispheres are small; in certain Fishes smaller than the optic
lobes; in the higher tribes they nearly or quite overlap both
olfactories and cerebellum. The brain may be smooth, as in most
cold-blooded animals, or greatly convoluted, as in Man.
Vertebrates are subdivided into five classes: _Fishes_, _Amphibians_,
_Reptiles_, _Birds_, and _Mammals_. The first three are cold-blooded,
the other two warm-blooded. Fishes and Amphibians agree in having gills
during all or a part of their lives. The rest never have gills.
2. FISHES, (_Pisces_.) These are considered the lowest of Vertebrates,
yet they are so numerous as to embrace nearly one half of all
Vertebrates, and so varied that it is difficult to frame a definition
which shall include them all.
Fishes live in the water and breathe by means of gills. They are
generally covered with scales, and they have fins instead of limbs. They
have large immovable eyes, but no external ears. Both jaws are movable.
The teeth are numerous, and are generally recurved spines, as in the
Pike; flat and triangular, with serrated edges, in the Shark; and
tessellated, in the Ray. The digestive tract is relatively shorter than
in other Vertebrates. The blood is red, and the heart has two cavities,
an auricle and a ventricle, both on the venous side. Ordinary fishes
have four gills, the water escaping by one external aperture, or
“gill-slit;” but in Sharks there is a separate opening for each gill.
[Illustration: FIG. 143.—Varieties of Fish Scales. _a._ Ctenoid scale.
_b._ Cycloid scale. _c._ Ganoid scale. _d._ Placoid scale. ]
There are four principal varieties of fish-scales. (Fig. 143.) 1.
Cycloid scales, (_cyclos_, a circle,) which are most common; thin,
flexible, and silvery, as in the Salmon. 2. Ctenoid, (_kteis_, a comb,)
with a comb-like fringe of toothed processes. 3. Ganoid, (_ganos_,
brightness,) generally larger than the preceding, and having an under
layer of bone with a superficial layer of enamel. Most ganoid fishes are
extinct. 4. Placoid, (_plax_, a flat plate;) these are formed of bony
granules, or tubercles, or plates, the plates often being furnished with
spines.
Most fishes have a series of small scales running along the side of the
body, called the lateral line. Each scale is perforated by a tube which
runs along the whole length of the body, and is connected with cavities
in the head which secrete the mucus for lubricating the scales, and
enabling the fish to move with little resistance.
Order 1. _Pharyngobranchs_, (_pharynx_, the pharynx, and _bragchia_,
gills.) This contains but one member, the Lancelet, (_Amphioxus
lanceolatus_,) which burrows in the mud of the Mediterranean Sea. It is
such an eccentric creature, without skeleton, limbs, brain, heart,
lymphatics, or red blood, that it can hardly be considered a Vertebrate
at all. Yet, because it has a persistent notochord, evolutionists have
made much ado over it, and it figures largely in their imaginary
_Phylogenies_. (Chap. III, Sec. 8.)
[Illustration: FIG. 144.—Lamprey.]
Order 2. _Marsipobranchs_, (_marsipos_, a pouch.) They have a
cartilaginous skeleton and sac-like gills, but no scales, limbs, or
lower jaw, and only one nasal organ. They comprise the eel-like Lampreys
and Hags. (Fig. 144.) The mouth is round and sucker-like; and in the
Hags (_Myxinæ_) contains a single large recurved, serrated fang for
piercing the bodies of their prey. Respiration is carried on by muscular
little pouches (_marsupia_) placed on the sides of the neck.
[Illustration: FIG. 145.—Gray Mullet: _a._ First dorsal fin. _b._
Second dorsal. _c._ Pectoral. _d._ Ventral. _e._ Anal. _f._ Caudal. ]
[Illustration: FIG. 146.—The Cod.]
Order 3. _Teleosts_, (_teleios_, perfect: _osteon_, a bone,) includes
all the true osseous fishes. The skull is complicated, the upper and
lower jaws complete, and the gills are comb-like, or tufted. The tail is
_homocercal_, having equal lobes. The other fins vary in number and
position. In the soft-finned Fishes, the ventral fins (Fig. 145) are
absent, as in the Eels; or attached to the abdomen, as in Salmon,
Herring, Pike, and Carp; or placed under the throat, as in the Cod,
(Fig. 146,) Haddock, and Flounder. In the spring-finned Fishes, the
ventrals are generally under or in front of the pectorals, and the
scales are ctenoid, as in the Perch, Mullet, and Mackerel.
[Illustration: FIG. 147.—The Sturgeon, (_Acipenser Sturio_.)]
Order 4. _Ganoids_ include the Sturgeons, (Fig. 147,) Bony-pike,
Polypterus, and many extinct forms. The skeleton is rarely completely
ossified; the ventral fins are placed far back, and the tail is
_heterocercal_, or unequally lobed, from the vertebra continuing in the
upper lobe.
Order 5. _Elasmobranchs_ (_elasma_, a thin plate) contain Sharks, Rays,
and Chimeræ. The gills are formed of thin laminæ, arranged like the
leaves of a book. They have a cartilaginous skeleton, and a harsh skin
called “shagreen.” The gill-openings are uncovered, and the mouth is
generally under the head, (except in the Chimeræ.) The ventral fins are
placed far back, the pectorals are large, and in the Rays enormously
developed and the tail is heterocercal.
[Illustration: FIG. 148.—Lepidosiren.]
Order 6. _Dipnoi_, (_dis_, twice; _pnœ_, breath,) comprises the
Mud-fishes (_Lepidosiren_) of tropical rivers. (Fig. 148.) They have
eel-like bodies covered with cycloid scales. Both ventral and pectoral
fins are present, but are small filiform organs, nowise resembling
ordinary fins. They have rudimentary external gills, and internal ones
which communicate with the exterior by a single slit. They also possess
true lungs, which communicate with the gullet by a tube or trachea. The
heart has two auricles and one ventricle. They are quite Amphibian in
structure, and live long out of the water.
3. CLASS II, AMPHIBIA, (_amphi_, both; _bios_, life,) receives its name
from the animals it contains being able to live both on land and water.
They are cold-blooded Vertebrates which breathe by gills during some
part of their life, but sooner or later possess lungs. Some retain their
gills through the whole of their life, as the Proteus, Siren, and
Axolotl; others lose their gills after a time, and breathe by lungs
only, as Frogs, Toads, and Newts. All undergo metamorphoses after
leaving the egg, passing through the “tadpole” state in which they
resemble Fishes in their respiration, circulation, and locomotion.
Order 1. _Urodela_, (_oura_, a tail; _delos_, visible,) the tailed
Amphibia. They have a naked skin, and two to four legs. The aquatic
Newts and land Salamanders drop their gills, and always have four limbs.
Order 2. _Labyrinthodontia_ (_labyrinthos_, a labyrinth, _odous_, a
tooth) are now all extinct. They resembled gigantic Salamanders, except
in their complex teeth and exoskeleton of bony plates.
Order 3. _Gymnophiona_, (_gymnos_, naked; _ophis_, a snake,) also called
Cecilia. They have neither tail nor limbs, a snake-like form, minute
scales in the skin, and numerous ribs.
[Illustration: FIG. 149.—1. Frog, (_Rana temporaria_.) 2. Toad, (_Bufo
vulgaris_.) 3. Tadpoles.]
Order 4. _Batrachia_, or _Anoura_. (Fig. 149.) (_Batrachos_, frog;
_ana_, without; _oura_ a tail.) These are tailless Amphibia, and
comprise Frogs and Toads. They have a naked, moist skin, ten vertebræ,
and no ribs. They have four limbs, the hinder longer than the fore-legs.
They have four fingers and five toes. The tongue is long, fixed at the
anterior, and doubled up. It can be thrown out rapidly as an organ of
prehension. The eggs are laid in the water, enveloped in a glairy mass,
and the tadpoles are like the Urodelans till the gill and tail are
absorbed. Frogs (_Rana_) have teeth in the upper jaw, and webbed feet.
Toads (_Bufo_) have neither teeth nor webbed feet.
4. CLASS III. REPTILIA, or Reptiles. These are air-breathing,
cold-blooded Vertebrates, differing from Fishes and Amphibians by never
having gills, and from Birds by being covered with horny scales, or bony
plates. The skeleton is ossified, and never cartilaginous. Most are
carnivorous, and teeth are present, except in Turtles, where a horny
sheath covers the jaws. The lungs are imperfectly cellular, and the
heart is three-chambered, containing two auricles and one ventricle,
which is sometimes divided by a partition. In all cases a mixture of
arterial and venous blood is circulated. The limbs, when present, have
three or more fingers as well as toes.
There are four orders of living and five of extinct Reptiles. The living
orders are Snakes, Lizards, Turtles, and Crocodiles.
[Illustration: FIG. 150.—1. Rock Snake, (_Python molurus_.) 2.
Spectacled Snake, (_Cobra de Capello_.) 3. Boa Constrictor.]
1.) _Ophidia_, or Snakes. (Fig. 150.) These have no visible limbs, but a
vast number of vertebræ. The Python has two hundred and ninety-one, the
Rattlesnake one hundred and ninety-four, and the Boa Constrictor three
hundred and five. They have immovable transparent eyelids. The tongue is
bifid (cleft) and extensile. The mouth is very dilatable, from the
number of joints in the lower jaw united only by ligament. The skin is
shed in one piece by reversing it. Snakes move well either on land or in
water.
[Illustration: FIG. 151.—A. Head of Harmless Snake. B. Heads of
Poisonous Snakes of different genera.]
Poisonous snakes, as Vipers and Rattlesnakes, usually have a triangular
head covered with small scales, a constriction, or neck, behind the
head, two or more fangs and few teeth, small eyes with vertical pupil,
and short, thick tail. In the harmless Snakes the head blends with the
neck, and is covered with plates, (Fig. 151,) the teeth are numerous in
both jaws, the pupil is round, and the tail tapering.
2.) _Lacertilia_, comprising Chameleons, Blindworms, and Lizards, are
distinguished from the other orders by possessing clavicles, and having
teeth not lodged in sockets, as in the Crocodiles. They are often like
Snakes with four limbs, each having five digits. Some have no
exoskeleton, but it is generally present in the shape of scales, or
horny plates, or spines. In the _Iguanidæ_ it is elevated into a crest,
or mane, of horny scales, covering also the throat-pouches. The _Draco
volans_, or Flying Lizard, has a cutaneous expansion from the false ribs
which enable it to take short flights through the air. The tongue is
bifid in many of this order, but in Chameleons it is a long, round,
muscular organ, clubbed at the end, and coated with a viscid secretion,
by means of which it catches great numbers of flies by shooting it out
with remarkable speed.
3. _Chelonia_, or Tortoises and Turtles. These resemble Amphibians in
some respects, but their structure is very peculiar. The exoskeleton
unites with the endoskeleton, forming the _carapace_, or case, which
includes the viscera and muscular system. The vertebræ are soldered
together and the ribs are expanded, making the walls of the carapace.
The ventral piece is called the _plastrom_, or sternum. (Fig. 152.)
[Illustration: FIG. 152.—Skeleton of Turtle.]
The Sea-turtles, as the edible Green Turtle and the Hawk’s-bill Turtle,
which furnishes the tortoise-shell of commerce, have the limbs formed
for paddles. The fresh-water forms, as the Snapping Turtle,
(_Chelydra_,) are amphibious, and have palmated feet. Land Tortoises
(_Testudo_) have short, clumsy limbs, fitted for slow motion on land.
[Illustration: FIG. 153.—1. Crocodile, (_Crocodilus vulgaris_.) 2.
Alligator, (_Alligator lucius_.) 3. Lizards.]
4. _Crocodilia_, or Crocodiles, Alligators, and Gavials. (Fig. 153.)
These are the largest Reptiles. They have a double exoskeleton, one of
horny scales, (epidermic,) and another of bony plates, (dermal.) The
bones of the skull are united by sutures, and the jaws are furnished
with numerous teeth implanted in distinct sockets. Crocodiles can be
distinguished from Alligators by the fourth tooth on the lower jaw being
larger than the rest, and by its projecting on each side of the snout.
The toes of Gavials and Crocodiles are fully webbed, but those of
Alligators are only half-webbed. Some Crocodiles in the Nile attain to a
length of twenty-five feet. The Gavials, or Crocodiles of the Ganges,
have the jaws produced to an enormous length.
5. CLASS IV. AVES, or Birds, are warm-blooded Vertebrates, clothed with
feathers.
The bones of Birds are very compact and ivory-like, yet lighter than
those of Reptiles or Mammals. Many parts of the skeleton are fused, or
anchylosed together. The lumbar vertebræ are wanting, but the neck
contains from nine to twenty-four vertebræ, rendering it quite flexible.
The sternum is strong, and in birds of flight possesses a median Keel,
(_carina_,) to afford an increase of space for attachment of the great
pectoral muscles. Hence these birds are called _carinatæ_. The skull
articulates with the spine by a single condyle, and with the lower jaw
by the intervention of a separate bone, as in Reptiles.
The beak is the bird’s principal organ of prehension, and differs in
shape according to habits and food. The pharynx is simple. The œsophagus
varies in different orders. Except in some aquatic birds, the food is
received first into a temporary stomach, or _crop_, which is largest in
grain-feeders. From this the œsophagus leads to the true digestive
stomach, which secretes the gastric juice, (_proventriculus_,) and leads
to the muscular stomach or gizzard, (_ventriculus bulbosus_.)
In flesh-feeders this is thin, but in grain-feeders it is a powerful
triturating organ. The small intestine is short in carnivorous birds and
long in others. The large intestine ends in a dilated sac, the _cloaca_,
which also receives the terminations of the urinary and generative
organs.
The trachea is furnished with two larynges; one at the upper part, as is
usual in animals, and one called the syrinx, which is the principal
organ of voice, at the bifurcation of the trachea into the two bronchi.
Every means are employed to render the respiration rapid and complete.
The lungs are large and cellular, and the bronchial tubes not only
divide continuously in them, but conduct air into the general cavity of
the abdomen and to the interior of many of the bones.
[Illustration: FIG. 154.—A. Ear coverts. B. Bastard wing. C. D. E. Wing
coverts. F. Primaries. G. Scapulars. H. Secondaries. L. Tail coverts.]
The feathers of birds are cutaneous growths, each formed on a vascular
papilla at the bottom of a pit, or follicle. They are composed, like
hair, of epithelial cells. Each feather consists of a quill, or barrel,
and a vane, or beard, which is composed of barbs and barbules. The
barbules, from contiguous barbs, hook into each other like the latch of
a door into its catch, so as to present an even and resisting surface to
the air. Feathers receive different names on different parts of the
bird’s body. The feathers clothing the body are called _clothing_
feathers; the great quill tail feathers, so useful in steering are the
_rectrices_; those lying over the humerus and scapular are the
_scapulars_; the proximal end of the ulna is covered with the
_tertiaries_; the distal end of the same bone with the _secondaries_;
while the bones of the hand support the _primaries_, which are largest
of all. Each quill often carries a little light feather just beneath the
commencement of the vane, the _accessory plume_, or _plumule_. These
form the greater, lesser, and under wing coverts. (Fig. 154.)
Order 1. _Natatores_, or Swimmers. These have the body boat-shaped, and
the feet more or less webbed.
One division of swimming birds is called _Brevipinnatæ_, (Short-wings,)
the feathers and wings being short. It includes the Penguins, Grebes,
Puffins, Guillemots, and Divers. In the Penguins the wings are too short
for flight. The legs are placed far back, and the wings assist the
webbed feet as paddles.
[Illustration: FIG. 155.—Common Tern.]
The Cormorants, Pelicans, Gulls, Petrels, and Terns (Fig. 155) form the
group of _Longipinnatæ_, or Long-wings. The beak is hooked and pointed,
the tip being often very hard. The Albatross, one of the largest and
most beautiful birds of flight, belongs to this group.
[Illustration: FIG. 156.—Wild Duck, (_Anas boschas_.) North America.]
The _Lamellirostres_, or Flat-bills, form a third division, including
Ducks, (Fig. 156,) Geese, Swans, and Flamingoes, whose bills are
horizontally compressed, covered with a soft cuticle supplied with twigs
from the fifth nerve, and have fringed sides, which strain the muddy
food.
Order 2. _Grallatores_, or Waders, (_grallæ_, stilts,) have long,
stilt-like legs, toes free, wings large and powerful.
The Rails, Coots, Water-hens, and Jacanas form a group called
_Macrodactylæ_, because the claws are very long. They are four in
number, and lobed. The beak is somewhat cuneiform, and the tail is very
short.
[Illustration: FIG. 157.—Heron.]
The _Cultirostres_, with elongated forcep-like bills for fishing,
include the Cranes, Herons, (Fig. 157,) Stilts, Ibis, and Spoonbills.
The legs are very long, and not covered with feathers.
The _Longirostres_, or Long-beaks, possess long and sensitive beaks,
grooved by nostrils. The legs are of moderate length. They are
insectivorous. The group comprises the Snipes, Woodcocks, Sandpipers,
Curlews, Ruffs, and Godwits.
The Plovers, Lapwings, Bustards, Longshanks, and Oyster-catchers form
the _Pressirostres_. All possess a moderate bill with a compressed tip.
Feet semi-palmate, wings long and strong.
Order 3. _Cursores_, or Runners. The wings are rudimentary and unfit for
flight. The legs are hollow, strong, and long. The order includes the
Ostriches, Cassowaries, and Apteryx, marked by their large size,
keelless breastbone, and robust legs. The African Ostrich has two toes,
the Cassowary three, and the Apteryx four. The barbs of the feathers are
disconnected, forming plumes.
[Illustration: FIG. 158.—Turkey, (_Meleagris Gallopavo_.)]
Order 4. _Rasores_, or _Gallinaceæ_, Scratchers, or Fowls. (Fig. 158.)
These have a short arched bill, and short and concave wings. There are
three anterior toes and one posterior. The anterior are blunt and
adapted to scratching. The gizzard is very strong. The legs are usually
feathered to the heel, and sometimes to the toes. The males have usually
gay plumage and some appendage to the head. Their principal food is
grain. The order comprises the common Fowl, Turkey, Partridge, Grouse,
Pheasant, Ptarmigan, and Pea-fowl.
The preceding orders form a legion called _Autophagi_, since immediately
on being hatched they can run about and look after themselves. The
remaining orders form the legion _Heterophagi_, in which the young are
dependent upon their mother for nourishment for some time after birth.
[Illustration: FIG. 159.—Wood-Pigeon.]
Order 5. _Columbæ_, or Pigeons. These differ from the Scratchers in
possessing powerful wings. They have slender legs, with toes ununited,
and the hind toe on a level with the rest. Pigeons, Doves, (Fig. 159,)
and the extinct Dodo are found in this order.
Pigeons exhibit in a great degree the mutability of races or varieties;
all the vast number of Pigeons, Carriers, Tumblers, and Fantails, being
descended from one common stock—the blue rock Pigeon, _Columba livia_.
Order 6. _Scansores_, or Climbers, have four toes, two directed forward
and two backward. They feed on insects or fruit. They are not usually
musical. The majority make nests in the hollows of old trees, but the
Cuckoos lay in the nests of other birds. In climbing, the Woodpeckers
are aided by their stiff tail, and the Parrots by their hooked bill.
Cuckoos, Parrots, Toucans, Trogons, Woodpeckers, and Wrynecks belong to
this order.
Order 7. _Passeres_, or Perchers, is the most numerous of all the
orders. The two outer toes are joined by membrane. Of the two others,
one is always directed backward. Females are generally smaller than
males, and have more somber colors. Their nests are often of beautiful
construction. The voice is often musical, the plumage lustrous, and the
power of flight perfect.
The _Conirostres_, (Cone-bills,) with a short, strong, roundish or
conical beak, which tapers rapidly from a broad base to a short tip,
includes the Finches, with the Sparrows, Larks, Crossbills, Crows, and
Hornbills. Birds of Paradise, also, and many migratory birds, as the
Starling, belong here.
The Shrikes, Fly-catchers, Nightingales, Orioles, Robins, Thrushes,
Tits, and Warblers form another group, the _Dentirostres_, or
notched-beaks, from having an abrupt notch on the margin of the upper
beak, near its tip.
The Humming-birds, Hoopoes, Wrens, Creepers, and Honey-eaters,
constitute the _Tenuirostres_, (Slender-beaks,) in which group the beak
is elongated into a slender forceps for extracting honey or insects from
the deep parts of flowers. The plumage is often of a gorgeous metallic
luster.
[Illustration: FIG. 160.—Swallow, (_Hirundo_.)]
The Swallows, (Fig. 160,) Martins, Goatsuckers, Kingfishers, and Swifts,
make up the _Fissirostres_, (Cleft-beaks,) with a wide but short beak.
During flight the mouth is kept wide open, and any insects it encounters
are retained by a viscid secretion. A young Swallow will in this way
consume over a thousand flies and gnats in a day.
[Illustration: FIG. 161.—Golden Eagle.]
Order 8. _Raptores_, or Raveners. These are readily recognized by their
beak, which is a formidable weapon with sharp edges and an acute hooked
tip. The upper bill overlaps the lower. The toes are three in front and
one behind, all terminated by sharp hooked talons. Wings, very large and
powerful. Legs, short, stout, and strong.
[Illustration: FIG. 162.—Barn Owl.]
There are two sections: the _Diurnal_, whose bright eyes are on the
sides of the head, wings pointed, and metatarsus and toes covered with
scales, as Vultures, Kites, Hawks, Falcons, and Eagles, (Fig. 161;) and
the _Nocturnal_, whose large eyes are directed forward, and surrounded
with radiating feathers, metatarsus feathered, plumage soft, as Owls.
(Fig. 162.)
6. CLASS V. MAMMALIA, or Mammals. These are warm-blooded Vertebrates
possessed of mammary glands. They suckle their young. The thorax and
abdomen are separated by a diaphragm, the red corpuscles of the blood
are doubly concave and round, (except in the Camel and the Llama,) and
either a part or all of the body is hairy.
All Mammals use their lips for prehension, which are assisted in some
orders by their fore-limbs. The Carnivora tear their prey with their
claws, but do not use them as prehensile organs. The proboscis of the
Elephant, the snout of the Tapir, the long viscid tongue of the
Ant-eater, and the long tongue of the Giraffe, are special prehensile
organs.
The teeth of Mammalia differ in the different orders, as to number,
size, and shape. The true Ant-eater has no teeth, the Narwhal has but
two, one of which is rudimentary, but the Dolphin has one hundred and
ninety. The Whalebone-whale (_Balæna mysticetus_) has, instead of true
teeth, a series of plates of whalebone ranged in rows along the upper
jaw. From these plates a long fringe of whalebone threads hangs down,
which acts as a sieve in straining the water from the myriads of little
mollusca which constitute the chief food of the whale.
There are three distinct types of stomach among Mammals: the simple, the
compound, and the complex stomach. The simple stomach is a single cavity
lined by epithelium, which secretes gastric juice. The compound stomach
has the cavity divided by folds into two or more spaces. The
tissue-elements, however, are the same throughout. The complex stomach
is peculiar to the Ruminants. It consists of four cavities: the
_paunch_—which is the largest cavity of all—to store the food and mix
it with the water it contains, and which in Camels, Llamas, and
Dromedaries contains pits closed by muscular rims for storing up fluid
when the animal is going a long arid journey; the _reticulum_, or
honey-comb apartment, where the food is made into small round pellets,
to be regurgitated into the mouth, where they undergo a second
mastication; the _manyplies_, with its mucous membrane arranged in
parallel folds, like the leaves of a book, and where some digestion of
soluble parts of the food may occur; and the _rennet_, or true digestive
stomach, where the albuminous principles of the food are extracted and
absorbed by the veins.
The digestive canal is much longer in herbivorous than in carnivorous
Mammals, being thirty times the length of the animal in the sheep, and
five times the length in the cat and dog.
An external ear is rarely absent; the eyes are always present, though
rudimentary in some burrowing animals; and, while in all other animals
the embryo is developed from the nourishment contained in the egg, in
Mammals it derives its support, almost from the beginning, directly from
the parent, and, after birth, is sustained for a time by the milk
secreted by the mammary glands.
Order 1. _Monotremata._ Includes two singular forms, the Duck-mole,
(_Ornithorhynchus_,) and Spiny Ant-eater, (_Echidna_,) both confined to
Australia. The former has a fur covering, a bill like a Duck, and webbed
feet. The latter is covered with spines, has a long, toothless snout,
like the Ant-eaters, and the feet are not webbed. Both burrow, and feed
upon insects.
[Illustration: FIG. 163.—Virginian Opossum.]
Order 2. _Marsupiala_, (_marsupos_, a pouch,) comprises Kangaroos,
Phalangers, Wombats, and Opossums, (Fig. 163.) Except the latter, all
are restricted to Australia and adjacent islands. The young are always
born prematurely, and are transferred by the mother to a pouch on the
abdomen, where they are attached to the nipples, and the milk is forced
into their mouths by special muscles.
[Illustration: FIG. 164.—Armadillo.]
Order 3. _Edentata_, (toothless.) This order contains very diverse
forms, as the leaf-eating Sloths and the insectivorous Ant-eaters and
Armadillos (Fig. 164) of South America, and the Pangolin and Orycteropus
of the Old World. The gigantic fossils Megatherium and Glyptodon belong
here. The Sloths and Ant-eaters are covered with coarse hair; the
Armadillos and Pangolins with an armor of plates, or scales. The
Ant-eaters and Pangolins are strictly edentate, or toothless; the rest
have molars, sometimes very numerous, wanting, however, enamel and
roots.
[Illustration: FIG. 165.—Skull of Rodent.]
Order 4. _Rodentia_, (gnawers.) These have two long curved incisors in
each jaw, which serve for gnawing the bark of trees, or other substances
on which the Rodent feeds. The front only is covered with enamel, and
the rest of the tooth is composed of softer dentine, which, wearing
faster than enamel, leaves a chisel-like edge to the tooth. Canine teeth
are wanting, and the flat molars are separated from the incisors by a
wide interval. (Fig. 165.) The hind legs of many Rodents, as the Hare
and Jerboa, are much longer and stronger than the fore-legs. Most of the
order are small in size, except the Capybara, Beaver, and Porcupine. The
order also contains Squirrels, Rats, Mice, and Agoutis. The Beaver has a
smooth, unconvoluted brain, yet shows great ingenuity in constructing
its dwelling, felling logs with its teeth, building them into a dam, and
arranging others as a shelter, plastering them with mud made into mortar
by its flat, trowel-like tail. The Flying-squirrel (_Pteromys_)
possesses a cloak of skin, stretching between the fore and hind limbs,
enabling it to sustain short flights in the air.
Order 5. _Insectivora_, (insect-eating.) These are diminutive animals,
as the Shrew, the Hedgehog, and the Mole. They have incisor, canine, and
molar teeth, and the latter have numerous pointed cusps. They have a
long muzzle, short legs, and clavicles. The feet are formed for walking
or grasping, and are plantigrade, five-toed, and clawed. The Hedgehogs
have a spiny exoskeleton, covering the entire body, and lined by a broad
muscle, which, when it contracts, rolls the animal into a ball.
[Illustration: FIG. 166.—The Skeleton of Bat. _cl._ Clavicle. _h._
Humerus. _cu._ Ulna. _c._ Radius. _ca._ Carpus. _po._ Thumb. _mc._
Metacarpus. _ph._ Phalanges. _o._ Scapula. _f._ Femur. _ti._ Tibia. ]
Order 6. _Cheiroptera_, (_cheir_, a hand; _pteron_, a wing,) are
distinguished by long fore-limbs, adapted for flight, the fingers being
very long, and united by a membraneous web. The toes and one or two of
the fingers are armed with hooked nails. The Bat may be called the only
true flying Mammal, since it is capable of rapid and long-continued
flights. (Fig. 166.) The Vampire-bat has a curious leaf-like expansion
of the skin covering the nose. The ears of Bats are very large, and
copiously supplied with nerves of touch. The sense of hearing is also
acute.
Order 7. _Cetacea_, (_Ketos_, a whale,) are fish-like in form and
habits. They are the largest of all living forms, and, next to the
Elephant, have the heaviest brains. The nostrils are on the top of the
head, and constitute the _blow holes_, or _spiracles_. This order
includes the Whales and Dolphins. All have a large horizontally
flattened caudal fin. The head is large, often forming half the bulk of
the animal. The Whalebone Whales (_Balænidæ_) are toothless, but in the
Greenland Whale, the largest of the group, which sometimes attains a
length of sixty or seventy feet, we find rudimentary teeth in the
embryo. The Toothed Whales (_Odontoceti_) have many conical teeth in the
lower jaw. The Sperm Whales are in this division. In them the head is
large and abruptly truncated, and the nostrils are at the end of the
muzzle. The _Delphinida_, comprising the Dolphins, Narwhals, and
Porpoises have teeth in both jaws. Many Cetacea have very small organs
of smell, and in the Dolphins and Porpoises they are wanting.
Order 8. _Sirenia_ (_seiren_, a siren, or Mermaid) are like the Cetacea
in shape, but are herbivorous, and frequent great rivers and estuaries.
They have both a temporary and permanent set of teeth, a narrow brain,
and nostrils on the top of a large snout. The Dugong and Manatee are
illustrations of this order.
Order 9. _Proboscidia_ include the Elephant, the extinct Mastodon, the
Dinothere, and the Mammoth. There are no canine teeth, but the incisors
are prolonged into tusks, which in the Elephant grow from the upper jaw,
in the Dinothere from the lower jaw, and in the Mastodon from both jaws.
The nose is prolonged into a long, flexible, sensitive trunk, which is
terminated by a small prehensile appendage like a finger. Cuvier counted
20,000 distinct muscles in an Elephant’s trunk. The limbs are massive,
each with five toes incased in hoofs, and with a thick pad intervening
between the toes and the ground.
Order 10. _Ungulata_, or Hoofed Quadrupeds, have four well-developed
limbs, each having not more than four complete toes, and each toe being
incased in a hoof. The leg is therefore for support and motion, and not
for prehension. They have temporary and permanent sets of teeth. The
_Odd-toed_ Ungulates include the Horse, the Rhinoceros, and the Tapir.
The Horse, which with the Ass and Zebra, made up the old order of
Solidungula, has only a single perfect toe on each foot, coated with a
nail, called a hoof, so that the horse walks and runs not merely on its
toes, but on its nails. The Rhinoceros has three toes on each foot, and
carries one or two horns on the skin of the nose.
The Tapir has four toes on its fore feet, and three on its hind feet, a
short snout, projecting nasal bones, and a short tail.
[Illustration: FIG. 167.—Stag.]
The _Even-toed_ Ungulates—the Hog, Hippopotamus, and Ruminants—have
two or four toes. The Hog and Hippopotamus have the four kinds of teeth:
incisors, canines, bicuspids, (or premolars,) and molars, and in the
wild state are vegetarian. The Ruminants have two toes on each foot,
enveloped in hoofs which face each other by a flat side, so as to appear
like a single hoof split, or cloven. There may be two supplementary
hoofs behind, but they do not usually touch the ground. All chew the cud
and have a complicated stomach. They have incisors in the lower jaw
only, and these are apparently eight; but the two outer ones are
canines. With few exceptions, as the Camel, all Ruminants have horns,
which are in pairs. Those of the Deer (Fig. 167) are solid, bony, and
deciduous; those of the Giraffe and Antelope are solid, horny, and
permanent; in the Goat, Sheep, and Ox they are hollow, horny, and
permanent.
Order 11. _Carnivora_, or Beasts of Prey, have four long, acute, canine
teeth, and there is a gap between the incisors and canines of the upper
jaw for the reception of the lower canine. There are usually six
incisors in each jaw. The digits always have sharp and pointed claws.
The body is covered with hair.
[Illustration: FIG. 168.—Toe of Lion. _a._ With the claw extended. _b._
_c._ Without the skin, retracted and extended.]
The order is divided according to the peculiarities of the limbs. (Fig.
168.)
The _Pinnigrada_ comprise the Seals and Walruses. The fore feet are
webbed and form paddles. The hind feet are at the end of the body,
enveloped in the integument, and in action they resemble the screw of a
steam-ship. They live on fish.
The _Plantigrada_ have the whole, or nearly the whole, of the hind foot
in the form of a sole, which rests on the ground. The claws are not
retractile; the ears are small, and tail short. Bears, Badgers, and
Raccoons are well-known examples.
[Illustration: FIG. 169.—Skeleton of the Lion, (_Felis Leo_.) C.
Cervical vertebræ. D. Dorsal vertebræ. L. Lumbar vertebræ. S. Sacral
vertebræ. C. _d._ Caudal vertebræ. _a._ Scapula. _b._ Humerus. _c._
Ulna. _d._ Radius. _e._ Metacarpus and phalanges. _f._ Ilium. _g._
Femur. _h._ Ischium. _i._ Patella. _k._ Tibia. _l._ Fibula. _m._ Tarsus.
_n._ Os Calcis. _o._ Metatarsus and phalanges.]
_Digitigrada_ walk on the tips of the toes, and keep the heel raised
above the ground. It includes the fierce and powerful Cats, Pole-cats,
Ferrets, Weasels, Dogs, Hyænas, Jackals, Otters, etc. The Cats,
(_Felidæ_,) embracing Lions, (Fig. 169,) Tigers, Leopards, Panthers, and
Cats, have retractile claws, and the radius rotates freely on the ulna.
They have also a prickly tongue.
Order 12. _Quadrumana_ (four-handed) differ from all other Mammals by
having each of their four limbs terminated by hands, in which the thumb
is opposable to the other digits. (Fig. 170.)
[Illustration: FIG. 170.—Quadrumana. Baboons.—1. Mandrill, (_Papio
maimon_.) 2. Chacma, (_Chacma Porcarius_.) Monkeys.—3. Mona,
(_Cercopithecus mona_.) 4. Howler, (_Mycetes_.) 5. Spider, (_Ateles_.)]
The order is subdivided according to the position of the nostrils, into
1. Strepsirhines, or Monkeys with twisted nostrils, as the Lemurs and
Aye-ayes, which are the lowest of the monkey tribe. 2. Platyrrhines, or
Monkeys with simple sub-terminal nostrils, as the Spider-monkeys. These
are South American, or New-World monkeys, with prehensile tails. The
Howling-monkey (_Mycetes_) has a curious modification of the larynx in
the shape of a bony drum attached to the hyoid bone, with which it
produces discordant shrieks. 3. Catarrhines, or monkeys with oblique
nostrils, approximating below, separating above, as the Gorilla and
Chimpanzee. This division includes the highest, or anthropoid Apes of
the Old World. They are all four-thumbed. The tail is not prehensile,
and is often quite rudimentary. The canine teeth are large. (Fig. 171.)
The arms are long; in the Chimpanzee reaching to the middle of the
tibia, when hanging down.
[Illustration: FIG. 171.—A. Skull of the Orang-outang. B. Skull of an
adult European.]
Order 13. _Bimana_, (two-handed,) contains but one genus and one
species: _Homo_, or Man. (Fig. 172.)
[Illustration: FIG. 172.—The Human Skeleton. _a._ Skull. _b. b._
Vertebral column, or Spine. _c._ Ribs. _d._ Sternum, or Chest bone. _e.
e._ Scapulæ, or Blade bones. _f. f._ Clavicles, or Collar bones. _g. g._
Pelvic, or Hip bones. _h. h._ Humeri, or Arm bones. _i._ Radius, and
_j._ Ulna, bones of fore-arm. _k._ Femur, or Thigh bone. _l._ Tibia, or
Large bone of leg. _m._ Fibula, or Small bone of leg. _n._ Calcaneum, or
Heel bone. _o._ Tarsal bones, or Bones of the foot. _p._ Carpal bones,
or Bones of the wrists. ]
Man differs from all animals in being an erect biped. The vertebrate
type, which in all other cases is horizontal, in him is vertical. No
other animal habitually stands erect; in no other are the fore-limbs
used exclusively for head purposes, and the hind pair solely for
locomotion. His limbs are parallel to the axis of his body, not
perpendicular. They are nearly equal in length, but the arms are always
a little shorter than the legs. In the Apes the arms reach below the
knee.
Man only has a finished hand, which is a perfect organ of touch, and
most versatile in movement. The foot is planted upon the ground by the
entire length of the sole. The Gorilla has an inferior hand and an
inferior foot. The hand is clumsier and with a shorter thumb than man’s,
and the foot is prehensile, and is not applied flat to the ground.
Man is peculiar in his dentition. His teeth are vertical, of nearly
uniform height, and close together. In every other animal the incisors
and canines are more or less inclined, the canines project, and there
are vacant spaces.
Man possesses two muscles (the _peroneus tertius_ and _extensor primi
internodii pollicis_) which are not found in the highest Apes. The
origin of two other muscles is in Man altogether different from Apes.
(The tibial origin for the _soleus_, and the calcaneal origin for the
_flexor brevis digitorum_.)
The human skull has a smooth rounded outline, elevated in front, and
devoid of crests. The cranium greatly predominates over the face, being
four to one. Man differs from all Apes in the absolute size of brain,
and in the greater complexity and less symmetrical arrangement of its
convolutions. The brain of the Gorilla scarcely amounts to one third in
volume or one half in weight of that of Man.
From purely morphological reasons, therefore, Man is entitled to rank as
a distinct order of Vertebrates. Other considerations, to be referred to
in the next chapter, show that he should be regarded as a distinct type.
CHAPTER XVI.
T H E H U M A N T Y P E .
The master-work, the end
Of all yet done; a creature, who, not prone
And brute as other creatures, but endued
With sanctity of reason, might erect
His stature, and upright with front serene
Govern the rest, self-knowing; and from thence
Magnanimous, to correspond with Heaven,
But grateful to acknowledge whence his good
Descends; thither with heart, and voice, and eyes
Directed in devotion, to adore
And worship God Supreme, who made him chief
Of all his works.—MILTON.
1. In the rapid panoramic survey of living forms, which is all our
limits will allow, we have mainly confined ourselves to structural
forms, barely glancing at the instinctive peculiarities which determine
these forms for special ends. It is necessary to supplement our review
by a reference to functions and endowments which the structure itself
may not always indicate.
2. Biology includes not only Anatomy and Physiology, but Psychology
also. “The naturalist studies the instincts of the Ants and the Bees.
When he attempts the history of Man, shall he put aside that which in
him represents these instincts? Evidently not. Consequently he must not
stop with the body. He must consider the intelligence which is in us,
and which, up to a certain point, we have in common with animals; he
must show that it is this element of our being which recognizes the
outer world, which judges, which aspires. His work will be very
imperfect if he neglects this something of which the nature escapes us,
but of which the power is such, that through it man has not only
vanquished all animals, whatever their defenses, their size, or their
strength, but he has overcome, and made to work as his servants, even
the immutable forces of the inanimate world.”[25]
3. We have seen that the lower animals partake of living structures and
organs, the same in essential character and objects as those of man.
Careful observation will show that they also possess many mental or
psychological endowments, such as we find in the human type. The
differences of animated nature are differences of degree rather than of
essential nature. So far as we can see, all animals have
self-consciousness and volition, and many exhibit unmistakable signs of
reason.
4. On page 283 is an outline plan of the psychical endowments of man,
with the objects constantly influencing him and the normal activities of
his being. It begins with the most general and elementary properties of
animal life, and rises to the highest special powers of human nature.
More than an outline cannot be attempted, since an elaborate exposition
would require a large volume.
5. It will be seen that we have given prominence to consciousness in the
plan referred to. This is because it is an essential condition of every
mental operation. It is the knowledge which the mind has of its own
operations.
Objective. SUBJECT. Subjective.
{ Spiritual Consciousness Will. }
{ and of Spiritual }
{ Rational Beings Judgment. }
{ Objects, and }
{ (the Good, Principles. Faith. }
{ Beautiful, \ / }
{ True, etc.) \ / }
{ Conscience. }
{ / \ }
{ / \ }
{ The Consciousness Fancy. }
{ Mind of Ideas, }
{ itself. Sentiments, Thought. }
{ Emotions, }
{ Imaginations. }
{ \ / } Efferent
Afferent { \ / } Actions,
Impressions,{ Memory. Perception. } deranged
interrupted { / \ } by Sleep,
by Disease { / \ } Intoxica-
or { / \ } tion, In-
Depravity. { Objects Consciousness Voluntary } sanity, &
{ of of Motion. } Disease.
{ Sense. Sensations. }
{ Obscure Ideas. }
{ Consciousness }
{ Organic of Instincts, or }
{ Sensibility. States of Body. Consensual }
{ Actions. }
{ The Consciousness }
{ Organic of Body— Involuntary }
{ Life. or of Self. Motion. }
In the general account of the nervous system (Chap. XV., Sec. 1) it was
stated that many motions were merely reflex and involuntary. Many such
motions are also without consciousness. It is probable that a very large
proportion of the movements of the lower animals are of this character.
Other motions depend on organic contractility responsive to an external
stimulus, as when a piece of muscular fiber contracts on being scratched
with a pin. Ciliary motions, the closure of the leaves of Venus’-flytrap
(_Dionæa_) on being touched by an insect, and the movements of the
Sensitive plant, may thus be accounted for. Some motions, as the sleep
of plants, depend on the periodicity of functional activities, and
others, as the bursting of seed-vessels, may be owing to Endosmose. Mere
movement, therefore, is far from indicating consciousness.
“How early does consciousness arise? If we interpret, as we are
constantly doing, the experience of lower animals by that of higher
ones, we should answer, With the very commencement of animal life.
Indeed, nothing but conventional sentiment would prevent our
attributing, under this method, a feeble consciousness to some plants.
If, however, we reason from the character of the nervous system, which
is undoubtedly the sole organ of consciousness, and from the stages in
development at which a conscious experience can enter as a profitable
factor, we shall be inclined to believe that consciousness especially
characterizes the Vertebrata, and appears first in the higher Articulata
and Mollusca. The phenomena of consciousness undoubtedly increase
greatly in vigor and in value as we pass up through the Vertebrata, and
this form of activity is, in its governing relations, collected and
specialized in the cerebrum.”[26]
Without attempting to dogmatize upon a subject so imperfectly known, we
may suggest that many of the habits of Ants, Bees, and even of animals
of a more primitive type, afford as good evidence of consciousness as
the actions of human creatures themselves.
6. The consciousness of self, or general corporeal sensitiveness, is the
earliest sign of individuality, or personal knowledge. This is previous
to the senses, and independent of the nervous system. It manifests
itself in animals without nerves, as the Polyps, and seems to be a
necessary attribute of animal life. Yet this most primitive and most
clearly innate faculty implies mind, for by it we know that our body is
_our_ body. The corporeal structure is an object of which the mind takes
cognizance. The presence of this sensitivity proves the existence of
something distinct from the body.
7. The consciousness of the physical conditions or states of the
body—as tonicity, languor, hunger, thirst, warmth, and cold—has been
termed common sensation, or _cœnæsthesis_. It is especially conducted,
at least in the higher animals, by the ganglionic or sympathetic system
of nerves. By means of the connection of this with the cerebro-spinal
system the various affections of the mind and body mutually act upon
each other, rendering the phenomena quite complex. Certain obscure
ideas, of which one may be said to be half-conscious, and which taken
together make up what we call the disposition or temper of a man, are
the result of organic sensibility acting upon the common sensation. What
Dr. Carpenter terms “consensual actions” may also originate here, as
well as from sensation proper. In this term that eminent physiologist
includes all the purely instinctive actions of the lower animals, which
make up, with the “reflex,” nearly all the animal functions in many
tribes, and which are peculiarly elaborate in their character and
wonderful in their results in Insects. Such automatic and involuntary
actions as vomiting excited by the sight of a loathsome object, a bad
smell, or a disagreeable taste, or laughter excited by tickling, are
also classed under this term.
8. Sensation, or special sense, is caused by an impression on certain
parts of the nervous system, which are hence called sensitive. For
sensation two things are necessary: an impressible state of the
sensitive organs, and a perception by the mind.
9. Perception is the evidence we have of external objects by means of
the senses. It is necessary that the organs and nerves be sound, or
false perceptions will result. Ringing noises in the ears, floating
specks before the eyes, and many spectral illusions, have their origin
in a diseased condition of the organs. Yet that perception is an
attribute of mind is evident from the fact that attention is required.
The senses may be impressed by their appropriate objects, but without
attention they are not perceived.
10. Memory implies a former conscious experience, either of a physical
or mental kind; its retention, revival, and recognition. The laws of
memory, as they are called, or circumstances which excite recollection,
have been enumerated, as resemblance, contiguity, cause, effect, and
contrast.
11. The mind itself may produce in the sphere of consciousness, ideas,
sentiments, emotions, and imaginations. For the manifestation of mental
phenomena it is doubtless important to have continuously healthy
nerve-structure and other bodily organs, since the most accomplished
artisan cannot exhibit his full powers with imperfect tools and
materials; yet as the injury or destruction of the implement is no proof
of the annihilation of the artisan, so the injury or even destruction of
the body may not affect the soul. The mind is popularly supposed to be
dependent on the brain, yet medical authorities show that every portion
of the brain has been, in one instance or another, destroyed or
disorganized without affecting what are supposed to be the corresponding
intellectual powers. Abercrombie tells of a lady in whom one half the
brain was disorganized, but who retained all her faculties to the last,
and many such instances are on record. There is no constant relation
between the integrity of mind and body. The mind may suffer intense
agony while the body is in perfect health, or remain in calm serenity
while the body is tortured or is losing its vital powers.
12. Ideas, in a general sense, refer to any thing present to the mind as
an object of thought, whether present really or representatively. Some
ideas are related to experience, as the principles of mathematics,
notions of figure, extension, number, time, and space. Others are
independent of sensible representation, as the ideas of good and evil,
just and unjust, true and false.
13. Sentiments refer to feelings of esteem, gratitude, patriotism, etc.,
but emotions to mental pleasure or pain. The emotions are often very
complex, and influence every part of the nature, physical and mental; as
hope, joy, melancholy, love, and anger.
14. Imagination is a term which represents the power which the mind has
of combining ideas. The images produced by this faculty are sometimes so
vivid as to affect the organs of sense, and occasion morbid sensual
delusions, as well as to influence the organs of motion, secretion, etc.
No proof could be more positive of the independent agency of the mind.
In its highest degree imagination leads to creative fancy, or poetic
power. In some of its flights it may encroach upon the prerogative of
conscience, and lead to self-deception unless held in check by the
precepts of Divine revelation.
15. Conscience has been called the moral sense, moral faculty, moral
judgment, and susceptibility of moral emotions. It may also be termed
the inspirational capacity of the soul. It is that faculty, or
combination of faculties, by means of which we have ideas of right and
wrong respecting actions, and corresponding feelings of approbation or
disapprobation. Faith, in the scriptural sense of the term, is not
belief, but the volitional activity of the mind in the sphere of the
conscience.
16. Judgment is the decision of the mind after comparison. It is
altogether a mental function. It is an act of the mind upon and within
itself.
17. Volition is the dominion exercised by the mind over itself,
employing or withholding its faculties in any particular action. It is
synonymous with free agency, and is an essential attribute of spirit,
since the very idea of spirit supposes self-action. Feuchtersleben
judiciously distinguishes between the essential freedom of the spirit
and the freedom of the spirit linked to the body. He shows that freedom
may, first, limit itself, so far as the spirit makes itself the slave of
sin or error; second, it may be limited by physical laws; third, it may
be limited by organization. As to the first, the free man is good and
wise; as to the second, powerful; as to the third, healthy.
18. This brief examination of human endowments shows as great a
difference between men and brutes as exists between animals and
vegetables, or between vegetables and the mineral world. It is
considered by many that each department of nature becomes higher through
the addition of something which the next below it did not possess, and
as the differences of the animal and vegetable world form successive
additions to a common original plan or system of organization, we find
foreshadowings or prophecies of the characteristics of higher forms.
Thus the regularity of the crystal suggests to the imagination the
organization of the plant, and the motions of plants foreshadow the
nervous system. Thus, too, the higher animals have vague and indistinct
analogies of the vast endowments of man.
19. The unity of man was generally conceded by the early naturalists,
but has been largely debated in recent times. Agassiz himself held to
different creations, although believing they were a unit as to
intellectual and moral nature. The discussion continued, until a few
years ago it appeared to be the settled creed of men of “advanced” views
to deny man’s unity. Yet one point after another has been changed,
until, in the language of Mr. Tylor,[27] “it may be asserted that the
doctrine of the unity of mankind now stands on a firmer basis than in
any previous ages.”
20. Respecting the antiquity of man upon the earth, it is very plain
that the differences between the Hebrew, Samaritan, and Greek Pentateuch
are such as to forbid any settlement of the question by a reference to
the Scriptures. Long before the modern discussions on this subject
biblical scholars doubted if it was the design of the Scriptures to
reveal either the antiquity of man or the age of the earth. Yet the
discovery of human remains at Abbeville and other places, the remains of
lake-dwellings in Switzerland, and the shell heaps in Denmark, are
nowise inconsistent with the view of a degradation of some races from a
more highly civilized condition. The ruins of ancient nations certainly
point to an early civilization which was remarkable for extent and
splendor. As to the time required for these changes, Dana, in his
“Manual of Geology,” says: “The evidence, as it at present stands, does
not necessitate the carrying of man back in past time, so much as the
bringing forward of the extinct animals toward our own time.”
21. The numerous varieties of the human species may be divided into four
principal races, which comprise secondary and mixed races, each
including a number of families and nations: 1st. The White race, also,
but erroneously, called Caucasian. Its original country, judging from
the comparison of languages and historic testimony, lay between the
Mediterranean, the Red Sea, the Indian Ocean, the steppes of Central
Asia, and the Himalaya Mountains. From thence it has spread into India,
Arabia, Syria, Asia Minor, and Egypt. 2d. The Red, inhabiting only
America. 3d. The Yellow, which has existed in China from remote
antiquity, and has spread into all countries inhabited by Mongolians.
4th. The Black, which belongs to Central and Western Africa, and is
distributed over the tropics from the east coast to Australia. It is
doubtful if either of these races represents the primitive type of man.
22. We close our brief survey of life with the religious sentiments of
the Psalmist: “I will praise thee; for I am fearfully and wonderfully
made: marvelous are thy works; and that my soul knoweth right well. My
substance was not hid from thee, when I was made in secret, and
curiously wrought in the lowest parts of the earth. Thine eyes did see
my substance, yet being imperfect; and in thy book all my members were
written, which in continuance were fashioned, when as yet there was none
of them. How precious also are thy thoughts unto me, O God! how great is
the sum of them! If I should count them, they are more in number than
the sand: when I awake, I am still with thee. . . . Search me, O God,
and know my heart; try me, and know my thoughts; and see if there be any
wicked way in me, and lead me in the way everlasting.”
FOOTNOTES
[1] Beale’s “Protoplasm.”
[2] Cook’s “Biology,” p. 227.
[3] “Agreement of Science and Revelation,” by the Author.
[4] Huxley’s “Anatomy of Invertebrated Animals.”
[5] “Protoplasm,” by Dr. L. Beale.
[6] Stricker’s “Manual of Histology.”
[7] Beale’s “Bioplasm.”
[8] Agassiz, “Methods of Study in Natural History.
[9] Johnson’s “Cyclopedia, Art. Darwinism.”
[10] “Anatomy of Invertebrated Animals.”
[11] Stricker’s “Manual of Histology.”
[12] Agassiz, “Methods of Study.”
[13] Carpenter’s “General and Comparative Physiology.”
[14] Agassiz, “Methods of Study.”
[15] Agassiz.
[16] Orton’s “Comparative Zoology.”
[17] Orton.
[18] Schlieden’s “Poetry of the Vegetable World.”
[19] “Heredity,” by Joseph Cook, p. 46.
[20] Cook’s “Biology.”
[21] “Ladies’ Botany,” by Dr. J. Lindley.
[22] Lubbock’s “Wild Flowers in Relation to Insects.”
[23] Agassiz.
[24] See Frontispiece.
[25] Quatrefage’s “Natural History of Man.”
[26] Bascom’s “Comparative Psychology.”
[27] Art., Anthropology, in Encyc. Brit., ninth edition.
INDEX.
Acineta, the, what, 16.
Acrogens, families of the, 109.
Actinozoa, the, 171, 177.
Agassiz on evolution, 41.
Agave, or aloe family, the, 129.
Algæ, families of the, 91.
Algæ, the higher, 99.
Amaryllidaceæ, (amaryllis family,) the, 128.
Amœboid movement, why so called, 29.
Amphibia, the, 242, 251.
Amphibia, why so called, 250.
Analogous, anatomical import of the term, 76.
Anatomy, import of the term, 9.
Anaxagoras, teachings of, 11.
Animal kingdom,
four primary divisions of the, 78.
subdivisions of the, 82.
Animals, souls of, 13.
Arachnoidiscus Ehrenbergii, the, 93.
Arrowroot family, the, 128.
Articulata, the, 213.
Articulates, construction of the, 78.
Arum family, the, 131.
Asteroidea, the, 185.
Atomic theory, the, noticed, 18.
Aves, or birds, 256.
Banana family, the, 127.
Beale, Dr., quotation from on life, 17.
Bichat’s definition of life, 12.
Bimana, import of the term, 278.
Biology,
import of the term, 9.
teachings of, 10, 25.
confirmatory of dualism, 11.
Bioplasm,
what, 26, 33.
how nourished, 26.
all animal life originated from, 27.
growth an essential property of, 30.
Birds, families of, 256.
Blood, circulation of the,
in vertebrates, 241.
in amphibia and reptiles, 242.
in birds and mammals, 242.
Botany, definition of the term, 9.
Brachiopod, the, 192, 196.
Bromeliaceæ family, (pine apple,) 128.
Carnivora, (beasts of prey,) the, 275.
Carpenter, Dr. W. B., his definition of life, 12.
Cephalopodæ, the, 192, 208.
Characeæ, the, 109.
Cœlenteratæ, the, 171.
Coleridge, on life, 12.
Comatulidæ, the, 185.
Confervæ, the, 91.
Coniferous plants, the, 142.
Conjugateæ, (stoneworts,) the, 91.
Conscience, 288.
Consciousness, 282.
Construction
of mollusks, 78.
of radiates, 78.
of vertebrates, 78.
Crustacea, the, 220.
Cuvier, his divisions of the animal kingdom, 78.
Cyperaceæ, the, 125.
Democritus, teachings of, 10.
Desmidiaceæ, family of the, 88.
Diatomaceæ, family of the, 92.
Diatoma vulgare, the, 95.
Dipnoi, the, 250.
Dualism, 10, 18, 37.
Echinodermata, (spiny-skinned,) the, 171, 184.
Edentata, (toothless,) the, 269.
Ehrenberg, Professor, on Vorticella., 14.
Electricity, powers of, 54.
Endogens, (to produce within,) the, 122, 132.
Equistaceæ, (horsetails,) the, 113.
Evolution,
import of the term, 40.
not a modern science, 41.
Agassiz on, 41.
Exogens, (to produce outward,) the, 137, 160.
Family, or tribe, a, what, 74.
Ferns, 114.
Fishes, 245.
Functional character of organs, 77.
Fungi, 103, 105, 106.
Gasteropoda, the, 192, 201.
Generations,
alternation of, 48.
three, modes of, 49.
Genus, what, 75.
Ginger family, the, 128.
Gramineæ, (grass family,) 124.
Grammataphora, the, 95.
Gregarinidæ, the, (parasitic plants,) 162.
Growth an essential property of bioplasm, 30.
Haeckel, on life, 12.
Heliopelta, (sun-shield,) the, 95.
Hepaticæ, (liverworts,) the, 112.
Homologous, import of the term, 76.
Horsetails, the, 109.
Human type, the, 281.
Hydra, why so called, 172.
Hydrozoa, the, 171.
Ideas, relations of, 287.
Imagination, the, faculty of, 288.
Inanimate things incapable of producing animate, 19.
Infusoria, the, 14, 16, 23, 24, 164.
Insecta, the, 227.
Invertebrates, nervous system of, 244.
Iridaceæ, (iris family,) the, 128.
Isthmia nervosa, the, 95.
Judgment, the, faculty of, 288.
Lamellibranchiata, the, 192, 196.
Leucippus, teachings of, 10.
Lichens, the, 101.
Life,
various definitions of, 12.
the result of power, 21.
Light, influence and action of, 54.
Lily family, the, 130.
Liverworts, (hepaticæ,) the, 109, 112.
Long-wings, the, 260.
Man, 281.
antiquity of, 290.
unity of, 289.
varieties of, 290.
Mammalia, the, 267.
Marantaceæ, (arrowroot family,) the, 128.
Marsipobranchs, the, 247.
Marsupiala, (pouch-bearers,) the, 269.
Memory, 286.
Molecular
movement, what, 29.
coalescence, what, 56.
Mollusca, the, 192.
Mollusks, construction of the, 78.
Monera, the, 162.
Monism, the theory of, 10, 17.
Morphology, import of term, 9.
Mosses, 116.
Navicula, the, 96.
Nervous system
of vertebrates, 242.
of invertebrates, 244.
Nostocs, what, 91.
Nutrition essential to life, 31.
Orchids, the, 129.
Order, an, what, 74.
Organic nature, unity of, 73.
Oscillatoria, what, 91.
Osmotic action, what, 55.
Palmellaceæ, family of the, 87.
Palmoglœa macrococca, the, 84.
Parentage, sexual and non-sexual, 43.
Park, Mungo, striking experience of, 120.
Partheno-genesis, what, 49.
Perception, faculty of, 286.
Pharyngobranchs, order of, 247.
Physiology, import of the term, 9.
Pigeon, 263.
Pine-apple family, the, 128.
Plato, teachings of, 11.
Polyzoa, (sea-moss,) the, 192.
Primitive forms of life, simple, 27.
Protococcus pluvialis, the, 85.
Protophytes, life-history of the, 84.
Protoplasm, physical basis of life, 28.
Protozoa, or primitive animals, 161.
Quadrumana, (four-handed,) the, 276.
Radiates,
construction of, 78.
how distinguished, 170.
Raveners, the, 265.
Reptiles, the circulation of the blood in, 245.
Reptilia, the, 252.
Resemblance, parental, 43.
Rhizopoda, what, 162.
Rodentia, (gnawers,) the, 270.
Runners, the, 262.
Science not opposed to revealed truth, 11.
Scratchers, or fowls, the, 262.
Screw-pine family, the, 131.
Scriptures, the, teach dualism, 11.
Sedges, the, 125.
Sensation, faculty of, 286.
Sentiments and Emotions, the, 288.
Short-wings, the, 259.
Species, a, what, 75.
Spencer’s definition of life, 12.
Sponges, the, 167.
Spontaneous motion a necessary accompaniment of life, 29.
Swimmers, the, 259.
Teleosts, the, 248.
Thallogens, families of the, 98.
Tissue, what, and how formed, 52.
Tunicata, the, 192, 195.
Type, a, what, 73, 75.
Urodela, the, 250.
Vegetable Kingdom, divisions of the, 81.
Vertebrates,
construction of 78, 239.
nervous system of the, 242.
Vertebrates, five classes of, 245.
Volition, what, 288.
Volvocineæ, family of the, 87.
Vorticella, the, 14, 16.
Waders, the, 260.
Worms, the, 214.
Zingiberaceæ, the, 128.
Zoospores, the, 88.
Transcriber’s Notes
Obvious errors in punctuation and in spelling, if the word was spelled
correctly elsewhere in the book, were silently corrected.
There were several NAMES spelled in unusual ways or even inconsistent
ways and these, along with possibly strange wordings, were left
unchanged.
On page 96, typo ‘naus’ was corrected to ‘navis’.
On pages 131 and 132, two consecutive, numbered subsections both are
numbered ‘11’ in the original. This has not been changed.
THE END.
[The end of _The Science of Life; or, Animal and Vegetable Biology_ by
J. H. (Joseph Henry) Wythe]