free edge, is beset with fine flexible crystalline points, arranged in
many successive rows, overlapping each other. The front, or attached
edge, is cut in a scolloped pattern, the extremities of undulations
that radiate from a common point behind the centre. The whole surface,
except the hinder portion that is studded with imbricated points, is
covered with an immense multitude of fine concentric lines, which follow
the form of the general outline. These are marks of successive increase;
for every one of the lines is the margin of a lamina, the aggregation of
which makes up the thickness of the scale. The laminae can be separated
by long maceration in water; and then we see that they are laid one on
another in regular order, the uppermost being the smallest, and the
first formed; the last made, which is the largest, being now in contact
with the skin.
[Illustration: SCALE OF GILTHEAD.]
Every scale is therefore a document, on which is indelibly written the
record of a multitude of processes, all effected in the past history of
the fish. The successively deposited laminae are exactly analogous to
those of calcareous substance in the shell of the bivalve;[81] and the
evidence is of exactly the same character as what we lately read off
from the valve of the _Dione_. But, just as in that example, too, the
overruling fact of recent creation precludes our deduction of time from
the evidence, since it proves the development to have been prochronic.
I see yonder a more terrific tyrant of the sea than the Sword-fish. It
is the grisly Shark (_Carcharodon_). How stealthily he glides along,
cutting the glittering surface of the sea with his dorsal, and now and
then protruding just the tip of the upper lobe of his caudal in the wake
of the other! Let us go and look into his mouth; for neither animals nor
elements present any impediments to these investigations of ours. Is not
this an awful array of knives and lancets? Is not this a case of
surgical instruments enough to make you shudder? What would be the
amputation of your leg to this row of triangular scalpels, each an inch
and a half in diameter? moved, too, by these powerful muscles?
But observe the arrangement of these most formidable teeth. They are not
confined to a single row as ours are, but each is succeeded by another
lying behind it, that by another, and another, and another,--why, there
are a dozen ranks of teeth, lying regularly packed one behind the other.
The object of this arrangement is a constant supply of new teeth, as
those in use become broken off, or wasted by the sloughing away of the
exterior half-ossified crust of the cartilaginous jaw, to which their
base is fastened by ligaments. Only one row, the outer one, is in use at
once, and this row stands erect; the others lie flat on each other (more
and more completely as they recede from the outer row); a reserve of
weapons in readiness for use, when those now employed are done with.
There is a continual growth of the surface to which the teeth are
fastened, from within outwards; so that each of the reserve rows will in
turn be brought to the edge of the jaw, when it will be thrown up into
the erect position, while the preceding, now turned out of the mouth by
the gradual eversion of the surface, sloughs away and disappears as an
useless incumbrance. It follows, therefore, that the teeth which we now
see erect and threatening, are the successors of former ones that have
passed away, and that they were once dormant like those we see behind
them.
But perhaps you may say, What evidence is there that these ever had any
predecessors? that they were not originally the front rank as they are
now? A very fair question.
In the first place, the great size of the tooth indicates maturity; and
is in keeping with the dimensions of the animal,--some twenty feet or
so,--which are those of an adult, if not a full-grown individual. But
adult age implies previous youth and infancy, and a gradual growth from
the length of a few inches to this formidable size. The teeth are found
in the embryo Shark when not more than a foot long; and it is evident
that many successive generations of teeth have passed away between those
pristine lancets of a line in diameter, and these of an inch and a half.
But stay; there is a peculiarity in the structure of these present
teeth, which surely indicates their place to be far on in the
succession. Each is seen to be finely serrated on its two outer
edges,--a provision which, of course, makes them more effective dividers
of flesh and bone. But this structure is not found in the teeth of young
individuals, which up to a period comparatively advanced, have simply
cutting edges.
Hence we are compelled by the phenomena to infer a long past existence
to this animal, which yet has been called into being within an hour.
On yonder twig sits a beautiful little Tree-frog, which you would be
ready to mistake for a leaf of more than usually emerald hue, but for
the glittering eye, and the line of yellow edged with purple that passes
down the side. Do you notice the frequent gulpings of the throat? Those
are the periodic inspirations Of air, by which the creature breathes;
for, having no ribs, by means of which to depress, and so to expand, the
thoracic cavity, the Frog swallows the air by a voluntary action. These
air-gulps afford us another example of the sort of evidence we are
searching for; they are so many proofs of a past history. For the
Tree-frog has not _always_ swallowed air; there was a period in its life
when it had no lungs; when it was an aquatic animal, as exclusively a
water-breather as any fish. Fish-like in _form_ it was then, as well as
in _habit_; it was a tadpole with a long compressed muscular tail, and
with external gills of several branches, but as destitute of lungs as it
was of limbs. Any physiologist, looking at our little green Tree-frog,
would pronounce without hesitation on the stages through which it has
passed; and would describe with the most perfect confidence the order
in which they took place; the gradual absorption of the branchiae, the
development of the lungs, the shrinking up and final disappearance of
the tail, the budding forth of the tiny rudimentary limbs, the hinder
pair first, then the fore pair, and the subsequent division of their
extremities into toes;--the metamorphosis of the little fish into a
little batrachian, and the gradual growth and maturation of the
latter,--these are facts,--the physiologist would say,--as sure both as
to their actuality and as to their order, as that the Frog is a Frog.
Ah! but the physiologist is not aware of a fact, which invalidates all
his conclusions based upon experience,--the fact that the little
Tree-frog has been created but this very instant.
Hark! that rattling noise is an admonition to us to tread circumspectly.
It is the vibration of the horny caudal appendages of a Rattlesnake. And
I see the reptile coiled up under yonder shadowing leaf. But our
presence is a privileged presence, and so we may handle and examine him
with impunity. The organ which produces this sound is composed of a
number of hollow horny capsules, each one fitting into the next, in
which it is retained loosely by a protuberance of its surface. These,
being agitated at the will of the animal, produce that sound which we
just now heard. The capsules are developed periodically, one being added
to the number already existing every year, until as many as forty are
accumulated.[82] This individual, therefore, having five-and-twenty
rattles, must be five-and-twenty years old.
This Snake, however, has had no past years; it has had no yesterday. Its
existence commenced this hour.
Here crouches, among the thick reeds, the Leviathan of the rivers, the
mailed Crocodile. His body, invested with bony ridged plates, that rise
into strong serrations along the tail, seems clothed with power; and his
long rows of interlocking teeth, unveiled by lips, appear grinning with
perpetual rage. An experienced herpetologist would not fail to find
many evidences of age in this huge reptile. First of all, he would point
to its monstrous size; then to the breadth and massive thickness of the
dermal plates. "The head," he would say, "in the ruggedness of its
surface, shows the same thing, for in youth it was comparatively smooth;
and also in the form of its outline; for in this example its length is
double its breadth, whereas in youth, these measurements were nearly
equal. These conical teeth, too, are by no means the same individual
teeth which existed at first. If you look at the base of one, you will
see that it is hollow, and that the sides of this portion are already in
process of absorption; that this hollow cone is a sheath for another
tooth beneath, which is destined to replace it; as this has itself
replaced its predecessor. The large size of the teeth which we see,
therefore, which accords with the dimensions of the jaws, is not a
condition induced by gradual growth, but by a succession of sloughings
and replacements; and hence the present teeth, in their size, point
conclusively to others which have preceded them, but which have
disappeared."
Yet nothing can be more certain, than that, in this Crocodile, which has
been created to-day, the successive teeth thus witnessed to, are but
ideal, that is prochronic, teeth; and that all the other indications of
the lapse of time, in the development of this individual, are liable to
the same exception.
See this solemn, slow-going Tortoise, shut up in his high-domed house of
bones. It is the beautiful _Testudo pardalis_, well named from the
plates being elegantly spotted and splashed with black on a pale-yellow
ground, like the fur of the panther. This is a rather large individual,
and the number of concentric lines on the plates of his armour,--or may
I not rather say the _tiles_ wherewith his house is roofed?--is
commensurately great. You see what I mean. Each of the angular plates
has a small nuclear lamina, not in the centre of the area, for the
development has been one-sided, but on the highest part. This was the
plate in its earliest form, or at least the earliest of which any trace
is left; for probably there were others yet earlier and smaller, which,
on account of their thinness, have been rubbed away in the travels of
the old wanderer. From this nucleus, the plate has been successively
enlarged, to correspond with the general growth of the animal, by
repeated additions of new laminae to the inferior surface; each new
lamina being a little wider in every direction than that which preceded
it, though not _equally_ on all the margins; and thus the plates assumed
the form of a very low cone, as you see, always preserving the specific
outline, and manifesting the stages of increase, by the projecting edges
of the successive laminae, exactly as we saw lately in the scales of the
fish.
[Illustration: PLATES OF TORTOISE.]
Whether these laminae are increased in an annual ratio, I am not sure,
nor is it important. There are, I find, about forty-five concentric
lines on one plate in this specimen, besides others which are
evanescent. Hence it would be quite legitimate to infer that this
Tortoise has passed through at least forty-five distinct periods of
life, each of which has left a legible record of its existence.
And yet, this moment, in which we look at it, is the very first moment
of its life; the concentric layers are evidences of processes that never
occurred, except prochronically.
See yonder stately bird, nearly of the height of man, marching among the
luxuriant musa-groves, and feeding on the succulent fruits. There is
nothing very admirable in its coarse, black, hair-like plumage; but the
rich hues of its naked neck, azure, purple, and scarlet, of the most
vivid intensity, attract the gaze. The most remarkable feature in its
physiognomy, is the singular, tall ridge of horn on its head, which,
like the crested helmet of some mailed warrior, imparts an air of
martial prowess to the bird, little in accordance with its peaceful
habits.
This protuberance is altogether a development of age. The skull, in the
youth of the Cassowary, was scarcely more elevated than that of a
chicken; but in the lapse of years, the bony ridge, encased in horn, has
gradually elevated itself to the height which it now possesses.
Here again we have a record of time, which is belied by the fact of the
bird's recent creation.
What is the glorious train of the Peacock, all filled with eyes, but a
false witness of the same kind? It leads us to infer that the bird is
three years old at least, since before that period, the covert feathers,
which are to form the splendid ornament of maturity, are not developed.
What are the lengthened tail-plumes of most refulgent blue, that adorn
the Fork-tailed Humming-bird (_Trochilus forficatus_); what the
gorgeously golden tail of the Resplendent Trogon; what the elegant
lyre-shaped feathers of the Menura; what the lustrous plumage of the
Birds of Paradise,--all of which have been but this hour created,--but
so many testimonies, unworthy of confidence, to a past history?
But, further, every individual feather of this beautiful array of
plumage concurs in bearing its unblushing witness to the same untruth.
What says the physiologist, who is able to read off these autographic
records?
[Illustration: GROWTH OF A FEATHER.]
"A little while ago, the tips of these feathers were seen each
protruding from the extremity of a thick, opaque tube; and a little
while before that, the tube itself, was a closed capsule, imbedded in a
deep follicle of the skin. If you had then cut open the capsule, you
would have found two concentric membranous tubes investing a highly
vascular secreting pulp, abundantly supplied with nerves and
blood-vessels through an orifice at the bottom of the capsule, and
destined to form the substance of the coming feather. Indeed, you would
have seen the soft, newly-formed barbs folded round the central
organized matrix; and below, the incipient quill, filled with the living
pulp-cells, and their blood-vessels, which were destined subsequently to
wither up and collapse into the light skinny pith which you see in the
perfectly matured feather. These are stages which each of these hundreds
of feathers has passed through; and these are but a single generation,
which have replaced former series that have been lost in the process of
moulting, every one of which had in its turn passed through exactly
corresponding stages, and so on backward, till we reach the first race
of feathers, which were already partly developed when the chick burst
forth from its imprisoning egg-shell."
So says the physiologist; but is he not most egregiously in error, since
this is the day of these lovely beings' creation?
There goes the great Whale, the true Whalebone Whale, rolling and
wallowing in the trough of the sea, and exposing his enormous black back
like an island amidst the white foam, which he stirs up, "making the
deep to be hoary." We will use our privilege and take a peep into his
mouth, as we did just now into that of the Shark.
What a cavern! and all bristling with long black hair! Why it seems as
if the hair grew on the wrong side of his head--on the inside instead of
the outside!
Nay, what you call hair is really the Whale's teeth, or what represents
teeth. This is the interior free fibrous margin of the _baleen_, which
descends in long triangular plates from the upper jaw. There are about
two hundred plates on each side, set face to face, with an interval
between, and the edges outward. The inward edge runs off into those long
hair-like filaments, which also extend from the slender tip. And the
whole forms an effective sifting apparatus, by which the volume of
sea-water, which the huge creature takes into his mouth in feeding, is
drained of the sea-blubbers, the worms, the mollusks, and other small
matters, which constitute the subsistence of this vast body.
Now each of these four hundred plates, some twelve feet in length, has
grown from a minute sort of bud, in the upper jaw. Its base is hollow,
resting on the formative pulp which is developed from the gum. The pulp
is understood to be the immediate origin of the hairy fringe, while a
dense vascular substance, seated between the bases of the plates, forms
the plate itself. When the plate reaches a certain length, its diameter
has become greatly attenuated, and its tip is constantly breaking away,
leaving the hair projecting. There is therefore a continual
disappearance of the substance of the plates at the tips, and a
continual growth at the base to supply the deficiency; and even more, at
least during the period of adolescence, because the actual dimensions of
the plates have to be increased in the ratio of the growth of the whole
animal.
Here, again, we read a record of past history. The Whale is known to be
a long-lived animal; and a period of many years must have passed in
bringing these plates of baleen to their present maturity. Yet the vast
organism before us has been created in its vastness but to-day.
On the most prominent shelf of yonder precipice, a sharp buttress of
naked limestone, stands an Ibex, guarding, like a watchful sentinel, the
herd in the sheltered valley which own his leadership. The pair of noble
horns, which are at once his defence and his pride, are marked
throughout their ample curve with semi-rings, or knobs, on their
anterior side. These afford us an infallible criterion of the animal's
age.
We can count in this Ibex fourteen of such prominent bosses. Now the
horn in these animals is not shed during life, but consists of a
persistent sheath of horny substance, enveloping a bony core. Until full
adult age, both the core of bone and the sheath of horn are continually
growing; and in the spring, when there is an unusual augmentation of
vital energy in the system, the increase is more than usually rapid. At
this season, the new matter deposited in the corneous sheath accumulates
in the form of one of these bosses, each of which is therefore produced
at the interval of a year. As the first boss appears in the second year
of the animal's age, we have but to add one to the number of the bosses
on each horn, and we have the number of years which it has lived. The
Ibex before us is just fifteen years old.
[Illustration: HORNS OF STAG;
In their successive developments.]
Yon Stag that is rubbing his branchy honours against a tree in the
glade,--can we apply the same criterion to him? Not exactly: for the
horns of all the Deer-tribe are of a different structure from those of
the _Capradae_. They are bones of great solidity, not invested with any
corneous sheath, but clothed for a certain portion of their duration
with a living vascular skin, and are shed every year during life and as
constantly renewed.
Yet the bony horns of the Stag are no less sure a criterion of age, at
least up to a certain period--than are those of the hollow-horned Ibex.
In the spring of the second year of the Fawn, the horns first appear,
seated on bony footstalks that spring from the frontal bone. The skin
that covers these knobs begins to swell and to become turgid with blood
supplied by enlarging arteries. Layers of bone are now deposited,
particle by particle, on the footstalks, with surprising rapidity,
producing the budding horns, which grow day by day, still covered by the
skin, which grows also in a corresponding ratio. This goes on till a
simple rod of bone is formed, without any branches. When this is
complete, the course of the arteries that supplied the skin is cut off
by fresh osseous particles deposited in a thick ring around the base.
The enveloping skin then dies, and is soon rubbed off.
After a few months, the connexion of the now dead bone with the living
is dissolved by absorption, and the horns fall off.
The next spring they are renewed again, but now with a branch or antler;
and the whole falls again in autumn. Every spring sees them renewed, but
always with an increase of development; and this increase is definite
and well-known; so that the age of a Stag, at least of one in the vigour
of life, can be readily and certainly stated.
For example, the individual Stag before us, now browsing so peacefully,
has each horn composed of the following elements:--the beam, or main
stem; two brow-antlers; one stem-antler, and a coronet of four snags, or
royal-antlers, at the summit. This condition is peculiar to the seventh
development, to which if we add one year for the hornless stage of
fawnhood, we obtain eight years, as, beyond all doubt, the age of this
Stag.
Both of these examples, however, the Ibex and the Stag, though so
conclusive, and seemingly so irrefragable, are rendered nugatory by the
opposing fact of a just recent creation.
See this Horse, a newly created, really wild Horse,
"Wild as the wild deer, and untaught,
With spur and bridle undefiled,"--
his sleek coat of a dun mouse-colour, with a black stripe running down
his back, and with a full black mane and tail. He has a wild spiteful
glance; and his eye, and his lips now and then drawn back displaying his
teeth, indicate no very amiable temper. Still, we want to look at those
teeth of his. Please to moderate your rancour, generous Dobbin, and let
us make an inspection of their condition!
Now notice these peculiarities. The third pair of permanent incisors
have appeared, and have attained the same level as their fellows; all
are marked with a central hollow on the crown, the middle pair faintly:
the canines have acquired considerable size; they present a
regularly-convex surface outwardly, without any marks of grooving on the
sides; their inner side is concave; their edges sharp; the third
permanent molar has displaced its predecessor of the milk set, and the
sixth is developed.[83]
This condition of the teeth infallibly marks the fifth year of the
Horse's age. A year ago the third incisor was only just rising; the
canines were small, and strongly grooved, and the third milk grinder was
yet existing. A year hence, the central incisors will be worn quite
flat, and their marks obliterated; the canines will be fully grown
tusks, the second molar will have reached its full height, and all the
teeth will be of the same level. We can then with perfect confidence
assert this to be a five-year old Horse. And yet, if we do so, we shall
assert a palpable untruth, for the young and vigorous stallion has been
created to-day.
[Illustration: SKULL OF BABIROUSSA.]
In the thickets of this nutmeg grove beside us there is a Babiroussa;
let us examine him. Here he is, almost submerged in this tepid pool.
Gentle swine with the circular tusk, please to open your pretty mouth!
Here are four incisors in the upper jaw; _at one time there were six_.
The canines of the same jaw having pierced through the flesh and skin
of the face, have grown upward and curved backward like horns; nay, they
have nearly completed a circle, and are threatening to re-enter the
skull; _once these tusks had not broken from the gums_. There are two
pre-molars: _once there were four_. There are three molars, of which the
first is worn quite smooth: _once this surface was crowned with four
cones; but the third molar had not then appeared_.
Away to a broader river. Here wallows and riots the huge Hippopotamus.
What can we make of his dentition? A strange array of teeth, indeed, is
here; as uncouth and hideous a set as you may hope to see. Yes, but the
group is instructive. We will take them in detail.
Look at the lower jaw first. Here are two large projecting incisors in
the middle, with their tips worn away obliquely on the outer side, by
the action of their opponents in the upper jaw, which are also worn
inwardly. The outer incisors, both above and below, are also mutually
worn in like manner. The lower canines form massive tusks, curved in the
arc of a circle, ground away obliquely by the upper pair; which are
short and similarly worn on their front edges. There are three
pre-molars on each side, below and above, much worn: once there was a
fourth, but it was shed early. Lastly, we find three molars, whose
crowns are ground down so as to expose two polished areas of a
four-lobed figure. A little while ago, these double areas were
trilobate, but at first there were no smooth areas at all; for these are
but sections, more or less advanced, of the conical knobs, with which
the crown of the molar was originally armed.[84]