“Bestimmt Die Gestalt die Lebensweise des Thieres
Und die Weise zu leben sie wirkt auf alle Gestalten
Mächtig Zurück.”—GÖTHE, _Metamorphose der Thiere_.
CORRESPONDENCE BETWEEN FORMS AND HABITS OF ANIMALS.
The most simple observation renders at once apparent a correspondence
between the external form of animals, the general direction of their
tendencies, and their habits.
Let us examine this question at somewhat greater length. From the
age of Aristotle to the present time, zoologists have arranged
the almost countless tribes of animals into a number of groups or
divisions, more or less related in general habits and structure. All
the classifications which have been hitherto proposed may be referred
to one or the other of two general principles. Either the colour of
the blood (Aristotle), the conformation of the heart (Hunter), the
arrangement of the nervous system (Owen), or some other peculiarity of
_internal_ structure, has been selected as the basis of arrangement;
or the animal creation has been grouped according to certain definite
circumstances connected with outward form and configuration. As
regards their internal organisation, the variations in the structure
and arrangement of the nervous system affords by far the best means
of classifying animals, and the whole animal world has accordingly
been divided into five primary divisions. We have already endeavoured
to prove that the manifestations of mind are only made known to us
through the medium of corporeal organs, whatever may be the nature of
its essence. By the state of the nervous system volition is modified or
controlled, the operation of the senses accelerated or retarded, the
muscular movements rendered feeble and uncertain, or strong, vigorous,
and energetic; in fine, the chief manifestations of life, thought,
volition, and independent motion, are all regulated by the condition
and structure of the central nervine masses.
APPENDAGES TO THE TRUNK A KEY TO THE ENTIRE ORGANISATION AND HABITS OF
ANIMALS.
The appendages to the trunk, like the arrangement of the nervous
system, furnish also a leading peculiarity of structure, and they may
be selected as the basis of a classification founded upon outward form.
For the most part, destined either for the purposes of locomotion,
or to assist in the procuring of food, they must of necessity be in
perfect accordance with the nervous and nutritive systems. Hence
the capacities, powers, and general habits of an animal, must be in
correspondence with this part of its organisation; so that when we
are acquainted with the form and arrangement of the extremities of an
animal, a key is thereby afforded to its entire organisation. Both its
external configuration, its mode of life, and its internal structure,
must harmonise, and be in accordance with the arrangement of the
extremities. Its breathing and vascular apparatus, its nutritive and
generative systems, are thus all indicated to us; and from a knowledge
of one particular we may safely and surely predicate the nature of the
rest.
_Annelida._—Thus in the worms (_Annelida_), creatures exhibiting but
few of the higher manifestations of life, we find the appendages
to the trunk in their simplest form,—that of fine, minute bristles
attached to the several rings or segments of the body. In the sea-mouse
(_Aphrodita_), their bristles attain a somewhat higher developement,
each of them being connected with a distinct elevation, or mammillary
process, with which it is, as it were, articulated.
_Myriapoda._—In the Centipedes, the first evidence of a well-formed
extremity makes its appearance in the form of numerous articulated legs
terminated by simple points. These legs, rudimentary in the lowest
species (_Iulidæ_), in harmony with their retiring habits and vegetable
diet, are divided into distinct joints, and provided with proper
muscles, in the strong and carnivorous varieties (_Scolopendridæ_). In
these latter animals, the ventral nervous ganglia are also increased
in size, in a ratio proportioned to the higher and more complex
structure of the appendages to the trunk.
_Insects._—In insects, creatures distinguished by so many and such
admirable instincts, and endowed with such active powers of locomotion,
the appendages to the body, both legs and wings, are perfectly and
beautifully formed. The former, six in number, are attached to the
three first thoracic segments of the body, composed of distinct
articulations, connected by ligaments and muscles, and furnished
with a series of minute breathing tubes, or tracheal ramifications,
extending throughout their entire substance. The latter—the wings—vary
much in their number, form, and arrangement; and it is upon characters
furnished by them that the nearest approximation to a perfect
classification of insects—that of Burmeister—is based. Thus, the legs
are typical of the class, the wings characterise the orders.
_Arachnida._—In the spider tribe (_Arachnida_) the legs, in their
general structure, resemble those of insects; but they are eight in
number, and, in addition to them, these creatures are provided with
remarkable claw-like appendages to their jaws—mere organs of feeling
in the mites, but strong and powerful instruments of prehension in the
scorpion tribe.
_Crustacea._—The crab and lobster tribe (_Crustaceans_) are likewise
accurately characterised by the appendages to the trunk, the number and
disposition of these parts having been employed by Milne Edwards for
the purpose of dividing these creatures into a number of orders.
_Mollusca._—Among the mollusks, the classes are nearly all named from
the peculiarities in form or the position of the feet. We have the
barnacles (_Cirrhopoda_), animals with six pair of articulated flexible
arms, composed of a series of small pieces studded with minute hairs,
and which form, when they are extended, a species of net by means of
which the animal catches its prey. The _Branchiopoda_—creatures such
as the _Terebratula_—with two long fleshy arms placed near the mouth,
which are hollow, muscular, and disposed in spiral folds. We have the
_Tunicata_, such as _Ascidians_ and the _Conchifera_, as the oyster and
mussel, beings which are destitute of members, and all but incapable
of locomotion. The _Gasteropoda_, of which the slug and snail afford
familiar examples, and that are furnished with a locomotive apparatus
peculiar to the whole class, and termed the foot or ventral disc. The
_Pteropoda_, nearly allied to the _Gasteropoda_ in their internal
organisation, but differing from them in the possession of two broad
fleshy expansions, resembling fins, which are attached to the side of
the neck, and are well adapted for swimming. And, lastly, we have the
_Cephalopoda_, such as the nautilus and cuttle-fish, creatures with
numerous strong muscular arms attached around the head, and in some
species provided with sucking discs, by means of which they are enabled
successfully to attack and capture the strongest and most active prey.
In all these instances we clearly see that the appendages characterise
the class, and that, from an acquaintance with their number and
arrangement, a naturalist could readily come to a conclusion as to the
affinities, structure, and general habits of any animal in the series.
_Fishes._—The fishes are divided into two great natural orders—those
furnished with a bony skeleton and those in which the framework of the
body is cartilaginous. The former division are distinguished by the
possession of a swimming bladder, and by the nearly equal developement
of the parts corresponding to the extremities—the pectoral and ventral
fins. The pectoral fins, situated immediately behind the head, are
present in all the osseous fishes, traces of them being found even
where they might be supposed to be entirely wanting, as in the eel;
they do not, however, attain any very considerable size, rarely
equalling, and never surpassing, the magnitude of the ventral fins.
In the cartilaginous fishes, on the contrary, not only in those which
ordinarily remain quiet at the bottom of the water, as the skate, the
sole, the flounder, and other flat fishes, but even in the active and
voracious sharks we find no swimming-bladder. In these cases, its
place is supplied and its duty performed by the enormously developed
anterior member or pectoral fin, which greatly surpasses the ventral
fin in size; and it is by means of the active movements of this large
hand that these creatures raise themselves from the bottom of the water
to the surface.
_Reptiles._—In the class of reptiles the characters afforded by
the form of the extremities are not less important. Of the four
orders into which this class is divided, one—that of the serpents
(_Ophidia_)—is altogether destitute of members, with the exception of
the rudimentary traces of extremities met with in some few species
(_Anguis_, _Bimanes_, and _Seps_). In another order, that of amphibious
animals (_Batrachia_), as the frogs, toads, &c., the extremities
are still typical of certain peculiarities of organisation. Some of
these creatures may be said to remain in an imperfectly developed or
embryonic condition during their whole existence. Instead of breathing
in adult life by means of lungs, as do the more perfectly organised
of the _batrachia_, they retain throughout existence that peculiar
structure of the respiratory apparatus—the branchial tufts—which
in the latter are present but in the embryo condition. In those of
the amphibious animals which breathe by means of permanent branchia
(_Perenni-branchiata_), such as the _Lepidosiren_ and the _Proteus_,
the extremities are either mere filamentary appendages, or at most
but very imperfectly-formed organs, and always typical of their
comparatively inferior organisation; while, in the higher species,
that is, those provided with lungs, and losing their branchiæ in the
adult state (_Caduci-branchiata_), as the frog, the salamander, &c.,
the extremities are well formed and perfectly developed. The third
order of reptiles—that of the lizard tribe (_Sauria_)—is made up of
members very dissimilar both in their appearance and general habits. In
the aquatic crocodiles the toes are connected by means of a membrane;
like ducks and other aquatic animals, these creatures are web-footed.
The alligator, so nearly allied to the crocodile in structure and
habits, with the exception that it is more terrestrial in its nature,
is furnished with a foot the toes of which are only webbed in half
their length, the other half being free and unconnected by membrane,
their amphibious mode of life being indicated by their foot. If we
compare the foot of these creatures with that of the true lizards,
the difference of structure will be found to be considerable. The
foot of the true lizard is provided with five toes to both the fore
and hind members, while attached to the hinder members of crocodiles
and alligators we find but four toes. The toes of the lizard are not
connected by a membrane, but are separate, and armed with nails,
for these creatures live on land, and have need of well-constructed
locomotive organs to enable them to catch their active prey. Among
lizards, that remarkable animal the chameleon, that is provided with
a particular structure of the skin, whereby its change of colour
is effected, is distinguished by the possession of a member, the
structure of which is not less peculiar. The toes are arranged in
two packets, which are capable of being brought into opposition—a
structure admirably adapted to the mode of life of the animal—the
climbing of trees and shrubs in pursuit of insects. The ichthyosaurus
and plesiosaurus, creatures of the lizard tribe which have now become
extinct, are both characterised by the form of their extremities.
The former has four members like paddles, each composed of nearly a
hundred small bones of an irregular polygonal shape and arranged in a
pavement-like form. The latter has also four paddle-shaped extremities,
but the number of bones of which each is composed is much less than in
the ichthyosaurus—not above fifty, the pieces being at the same time of
a different shape, and not arranged in a tessellated form.
_Birds._—Among birds the foot is a most important organ, serving
at once for support, prehension, and locomotion. Its modifications
are accordingly very numerous, and ornithologists have employed the
characters presented by it as a basis of classification. Scopoli, in
his Introduction to Natural History (1777), proposed a systematic
distribution of birds into two divisions founded upon the form of the
scales covering the foot; thus, some are furnished with scales, small
and polygonal (_Retepedes_), while others (_Scutipedes_) have the
legs covered in front with unequal semicircular plates. So, again,
in the division of birds proposed by Nitzsch, viz. into the aerial,
terrestrial, and aquatic, the foot will at once serve to indicate the
different orders. We will proceed to examine the special characters
afforded by the foot of birds in each of the groups or orders, adopting
the classification of Kirby, one of the most recent.
In the first order, the birds of prey (_Raptores_), which includes the
eagle, the vulture, the owl, &c., for the purpose of striking their
quarry, and of securing it by a firm grasp, a strong muscular foot is
necessary, and we consequently find that the foot is provided with four
short muscular toes, three placed before, and one behind, all armed
with long, sharp, hooked talons, those of the thumb and innermost toe
being the longest, as the great duty of grasping is mainly performed
by them. The claws are also capable of being drawn back, they are
retractile like those of the cat; and the scales upon the upper surface
of the foot, as well as the skin covering it below, are strong and
tough for the purpose of protecting the member from the attacks of the
living prey upon which these creatures feed. The foot is also broadly
marked, the kind of marking and the size of the scales being especially
characteristic of the different genera and families. In the vultures,
which from their feeding on carrion do not require such strength of
foot, we find a notable deviation from this general character, the toes
becoming longer and slighter and the claws much weaker.
In the second order of birds, the perchers (_Passeres_ of Linnæus),
which comprehends sparrows, thrushes, larks, &c., the foot is
constructed for another and a very different purpose. Its chief office
is to support the bird in a horizontal position upon the boughs
and branches of trees and shrubs; hence the foot is long, the toes
slender, very flexible, and armed with long, straight, weak claws,
which are not at all retractile. All the birds of this order possess
four toes, one of which, the hind toe (_hallux_), is placed straight
out behind, the others being in front, and those situated externally
are connected to the middle ones at their bases. The scales covering
the foot are regularly disposed, and as they are not needed for the
purpose of defence, they are thin and tender, resembling ordinary scarf
skin. Even in the shrikes,—the birds of prey of this order, who feed
upon living creatures and use the foot for securing them, the claws
are not sharp, nor is the foot formed in such a manner as to ensure
a very secure grasp, and we accordingly find that they merely press
this organ upon their prey for the purpose of holding it. In a few
other families of this order, as the todies, the kingfishers, &c., the
foot is called upon to assist in feeding, and we consequently find
certain modifications of structure indicative of this office. In order
to strengthen the foot and to secure a firmer grasp, the external and
middle toes are united almost to the apex, and the strength of the hind
toe is considerably increased.
In the third order, the climbers (_Scansores_), or, as they have been
sometimes termed, the yoke-footed, to which the woodpecker and the
parrot tribe belong, the structure of the foot is modified for the
important purpose of enabling the creature to support itself in all
positions upon the stems and branches of trees. In order to effect
this the foot is made strong, short, and muscular, the claws sharp
and curved, and the toes are placed in a very different position to
that which they occupy in other orders, two of them being situated in
front and two behind. By such a disposition, a strong, secure grasp is
afforded; and thus it is that most birds belonging to this order are
enabled to climb in a vertical position, and to effect movements like
animals of the monkey tribe. In general these birds move very awkwardly
upon a level surface, but in one or two species the structure of the
foot is so modified that they can run upon the ground with great speed.
This is the case with the travellers’ friend of South America, and
with the ground parrot of New South Wales; and these creatures have
accordingly slender toes so constructed, that one of the two placed
behind can be brought in front at will, so that a larger and more
secure basis of support is thus afforded.
In the fourth order the scratchers (_Rasores_), to which the common
fowl, the pheasant, and the pigeon belong, the foot is adapted for
an instrument of active locomotion, as well as for the purpose of
procuring food by scratching in the earth. Hence we find it strong,
with a long muscular leg, and four toes, three before and one behind,
covered with broad scales and armed with short claws. The thumb, so
necessary for perching and climbing, is in birds of this order short,
rudimentary, and attached high up in the leg, so that the whole foot
being placed flat upon the ground, affords a very firm support to the
animal.
In the fifth order of birds, the runners (_Cursores_), to which the
ostrich, the emu, and the cassowary belong, the structure of the foot
is wholly that of a powerful instrument of locomotion. The leg is
long, the thigh strong and muscular, and the foot short and compact.
The toes which never exceed two or three in number, and of which
the second is the largest, are placed all in front, and armed with
very short claws, or, as in the African ostrich, with the outer toe
destitute of a claw. The scales are limited to the upper surface of the
foot, the under surface being flexible and occupied by an elastic pad
upon which the member rests. Such a conformation of limb, which would
be wholly useless for perching or climbing, is admirably fitted for
running—witness the swiftness of the ostrich—a creature equalling and
even surpassing the fleetest horse in speed.
In the sixth order, the waders (_Grallatores_), or stilt birds, as
the stork, the crane, the heron, &c., the leg is long and slender,
and the foot weak and covered with shield-shaped scales. The toes,
four in number, are long and straight, three being placed anteriorly,
and a shorter one (wanting in the plovers and lapwings) behind; they
are frequently palmated at their base, as in the stork; or, as in
the middle claw of the heron, toothed or notched like a saw; while
sometimes they have a narrow-winged appendage, running along the side,
as in the sandpipers. In search of their food, insects and small fish,
the individuals of this order frequent marshy places and shallow
waters, and many of them, as the stork and heron, are remarkable for
the unerring certainty with which they strike and seize their small
finny prey.
In the last order, the swimmers (_Natatores_), called also web-footed
birds, to which the goose, duck, and gull belong, the foot is modified
to assist in swimming. The legs are short; the four toes, all placed
in front, are united by a broad membranous expansion, and armed with
claws, the thumb being likewise brought in front, so that a greater
extent of surface may be given to this oar-like member. A foot
thus constructed would be wholly unsuited for perching, running, or
grasping, but it is well adapted to the wants and habits of these
aquatic birds.
_Mammals._—It is but in animals who suckle their young (_Mammalia_)
that the extremities attain their greatest state of developement, and
it is in the higher orders alone that they become useful as organs of
prehension, their office being limited in most of the lower tribes to
support and locomotion. In the lowest order of the series, or whale
tribe (_Cetacea_), the members, in the number of pieces of which they
are composed, bear a considerable resemblance to the fins of fishes,
though they are somewhat differently constructed, according as the
animal may be destined exclusively for an aquatic existence, like the
common sperm whale, or be more or less herbivorous, and consequently
terrestrial in its habits, like the dugong. In the former case, the
extremities are converted into broad paddles adapted for swimming, and
the feet are webbed; in the latter, the members are better developed,
the toes being free, and furnished with nails at their termination.
Of those orders of _Mammalia_ which are provided with four members—the
ordinary quadrupeds—some are furnished with a foot which appears to
be entirely without toes, their place being supplied by a mass of
horny tissue—the hoof. This is the case with the ruminants—animals
that chew the cud—as the cow, and with the horse; but in the latter,
as the name of the order implies (_Solidungula_), the hoof is solid,
while in the ruminants it is cleft; and hence by some naturalists these
latter animals have been termed _Bisulca_. Some slight differences
are perceptible in the construction of the feet of ruminants: thus
the chamois, the antelope, and other of the deer tribe, are furnished
with an additional toe, which, projecting backwards, affords a firmer
support to the body. In the thick-skinned animals (_Pachydermata_) the
toes can hardly be said to be free, being still partially enclosed in
the tough skin. It is from characters afforded by the foot that several
tribes of animals belonging to this order are mainly characterised:
thus the elephant has five toes to each foot, the rhinoceros three,
and the hog and hippopotamus four. Among those of the mammalia which
are characterised by the presence of four members with distinct and
separate toes and nails, but few are furnished with a true hand—that
is, a member with a thumb capable of being brought into apposition with
the other fingers. Carnivorous animals have either a foot with sharp
recurved and retractile claws, as the cat and tiger, or with straight
blunt claws, not retractile, as the bear; or the feet are small, almost
completely enveloped in the skin, and furnished with a membranous
expansion connecting the toes, as in the aquatic seal and walrus,
or river-horse: but in all these animals, although the fore-legs may
be more or less employed as instruments of prehension, they are not
used for the purpose of conveying food to the mouth. In some of the
gnawing animals, as the squirrel, the anterior extremity commences to
assume the function of a hand; and in a few of the kangaroo tribe,
such as the opossum, the hinder extremities are provided with a thumb
capable of being brought into apposition with the other toes. The hand
of bats, which serves these animals not merely for flying, but also
supplies the place of eyes and ears, enabling them to avoid objects
during the obscurity of night, is furnished with a sense of touch
extremely delicate. It is in man and the monkey tribe only that we
meet with a true and perfect hand. In the latter, both the fore and
hind extremities are constructed upon the same general principle as
the hand of man; and hence these animals have been styled four-handed
(_Quadrumana_).
“In man the upper members are disposed in a manner the most favourable
for the exercise of their functions as organs of prehension and of
touch: the fingers are long and flexible; they have all, with the
occasional exception of the ring-finger, separate movements, which
other animals (even those provided with hands) have not; the thumb,
which is apposable to these latter, is longer in proportion to the
fingers than in monkeys, and consequently can more readily apply itself
to the extremity of their palm or surface, and better seize small
objects. The nails, which are large and flat, cover the back part only
of the extremity of the fingers, so as to furnish a support to the
organs of touch without in the least depriving them of their delicacy.
The entire hand can execute rotatory movements the most extended; and
to the arm which supports it is afforded a solid attachment by means of
a large shoulder or blade-bone and a long collar-bone.” The statement
of Milne Edwards,[3] then, does not appear far removed from the truth,
“That the faculties of the _Mammalia_ are the more elevated in
proportion as their members are the better constructed for prehension
and for touch.”
USE OF A KNOWLEDGE OF THE FORM OF APPENDAGES TO TRUNKS IN GEOLOGY.
A knowledge of the form of the appendages to the trunk of animals is of
great service to the geologist, for it has been well and truly said,
that the organic remains imbedded in rocks are as medals struck in
commemoration of the great revolutions which the earth has undergone,
and so small a portion as the extremity of an animal is sufficient to
indicate its nature, and to enable us to ascertain the class and order
to which it belongs. Let us take a few examples. Some fossil bones
were discovered by General Washington near his seat in Virginia. Mr.
Jefferson, by whom they were examined, stated that they had belonged
to an enormous carnivorous animal, which from the size of its claws he
named the _Megalonyx_. Upon an examination more carefully conducted by
Cuvier, it was found that in the paw the second bone of the toe was
symmetrical, while in animal feeders furnished with retractile claws it
is curved, and not symmetrical; the first bone, too, was the shortest,
whereas in the lion and others of the feline tribe it is the longest.
Whence Cuvier was led to conclude that the creature in question was a
sloth of large dimensions, which fed only upon plants.
Upon another occasion, from a careful consideration of the form and
size of a toe found in the Palatinate, near Eppelsheim, Cuvier was able
to determine that the animal to which it belonged was of the edentate
tribe of _Pangolins_. It was from an examination of the hand that
Cuvier decided upon the nature of the _Pterodactylus_. This curious
animal partook of the nature of both the reptile and the bird. Like
the bird, it was furnished with a long neck and a horny beak, but in
its jaws and teeth it resembled the crocodile. It had not, however,
like the bird, feathered wings without fingers to strengthen them, nor
had it a wing in which the thumb alone is free, like that of the bat.
Instead of the bony pieces of all the fingers being equally prolonged,
the second finger only was extended to a great length, and from it the
wing spread out, the other fingers being short and furnished with nails
like the toes of ordinary animals. Collini, its discoverer, supposed it
to be of marine origin; Soemmerring contended that it was a mammal; but
its true place in the animal series was first assigned to it by Cuvier,
who has satisfactorily shewn that it is in fact intermediate between a
bird and a reptile.
A knowledge of the form of the extremities of animals has been of great
service to palæontology in another way—in proving the existence of
certain species of animals at given periods of the earth’s formation,
from the print of their footsteps left upon the sand or other
material of the strata while it was yet in a soft state. Such traces
were first observed by Dr. Duncan in Dumfries-shire. On examining a
sandstone quarry, he found these prints not on one only, but on several
successive layers of the stone; so that they must have been made at
periods distant from each other. Similar impressions have been since
observed in the Forest marble-beds near Bath, at Hessburg in Saxony, in
the State of Connecticut, and in some other parts of the world.
“The marks found in Dumfries-shire, of which there were as many as
twenty-four upon a single slab, formed as it were a regular track,
with six distinct repetitions of each foot, the fore and hind feet
having left different impressions, and even the marks of the claws
being discernible. They appear to have been made by some animal of the
tortoise kind. At Hessburg the impressions were discovered in quarries
of grey and red sandstone alternating; and the marks were both larger
and more distinct than those found in Scotland. In one the hind foot
measured twelve inches in length, and the fore foot always appeared
much smaller than the hind. From this circumstance, and from the
distance between the two being only fourteen inches, it is conjectured
that the animal was a marsupial like the kangaroo, and it has been
termed by Dr. Kaup _Chirotherium_, from the supposed resemblance of the
four toes and turned-out thumb to a hand. In the State of Connecticut,
near Northampton, footsteps differing exceedingly in size have been
found in inclined strata of sandstone. They were evidently made before
it assumed its present position. The marks are always in pairs, and the
tracts cross each other like those of ducks on the margin of a muddy
pond. One is of the length of fifteen or sixteen inches, and a feathery
spur or appendage appears to have been attached to the heel, eight or
nine inches long. The distance between the steps is proportioned to
their length, but in every case the pace appears to have been longer
than that of the existing species of birds to which they approach
nearest—the ostrich, and the animal must consequently have been
proportionably larger. How much larger he was than the ostrich may be
gathered from this, that the large African ostrich has only a foot ten
inches long, less than two-thirds that of this bird, and yet stands
nine feet high. These proportions would give a height of fourteen feet
to the extinct animal.”[4]
The characters afforded by the foot have recently enabled Mr.
Strickland to determine that the dodo, a bird now extinct, is not
related either to the gallinaceous birds,—the vulture or the ostriches
as some have conjectured,—but is closely allied to the pigeons.
From this cursory examination of the animal world we may gather the
important conclusion, that from the structure of an extremity we may
obtain a complete insight into the entire organisation of an animal;
and thus the paws furnished with sharp retractile claws of the lion
indicate at once to a naturalist its strong teeth, its powerful
jaws, and its muscular strength of limb; while from the cleft foot
of the cow, the complicated structure of its stomach, the definite
peculiarities of its jaws, and its vegetable diet, may with equal
certainty be predicated.
Thus, as Paley justly observes, “In the swan, the web foot, the spoon
bill, the long neck, the thick down, the graminivorous stomach, have
all a relation to one another, inasmuch as they all concur in one
design, that of supplying the occasions of an aquatic fowl, floating
upon the surface of shallow parts of water, and seeking its food at
the bottom. Begin with any one of these peculiarities of structure, and
observe how the rest follow it. The web foot qualifies the bird for
swimming, the spoon bill enables it to graze. But how is an animal,
floating upon the surface of pools of water, to gaze at the bottom
except by the mediation of a long neck? And a long neck is accordingly
given to it. Again, a warm-blooded animal, which was to pass its life
upon water, required a defence against the coldness of that element.
Such a defence is furnished to the swan in the muff in which its body
is wrapped. But all this outward apparatus would have been in vain if
the intestinal system had not been suited to the digestion of vegetable
substances.”[5]
And, again, of the mole: “The form of the feet fixes the character of
the animal. They are so many shovels; they determine its action to
that of rooting in the ground; and every thing about its body agrees
with this destination. The cylindrical figure of the mole, as well as
the compactness of its form, arising from the terseness of its limbs,
proportionally lessens its labour; because, according to its bulk, it
thereby requires the least possible quantity of earth to be removed for
its progress. It has nearly the same structure of the face and jaws
as a swine, and the same office for them. The nose is sharp, slender,
tendinous, strong; with a pair of nerves going down to the end of it.
The plush covering, which, by the smoothness, closeness, and polish of
the short piles that compose it, rejects the adhesion of almost every
species of earth, defends the animal from cold and wet, and from the
impediment which it would experience by the mould sticking to its body.
From soils of all kind the little pioneer comes forth bright and clean.
Inhabiting dirt, it is of all animals the neatest.”