The great dilated lip, and the long finger-like processes of its edge, had no existence in the youthful days of the sh.e.l.l; they are marks of adult age: when young, the sh.e.l.l was simply spiral, with a thin straight lip bounding a narrow aperture.

Observe also a far more beautiful creature by its side, the Tiger Cowry (_Cypraea tigris_). Its sh.e.l.l is now entirely enveloped in the meeting wings of the great fleshy mantle, which is mottled with changing hues; and its foot or crawling disk covers a s.p.a.ce three or four times as large as the sh.e.l.l. On lifting it in our hand, the whole of this array of soft flesh has been rapidly retracted, and has wholly disappeared within that very narrow orifice, bordered with toothed projections, on the under side of the sh.e.l.l, which we can hardly believe capable of receiving a twentieth part of the bulk that has vanished within it. And now we see nothing but the sh.e.l.l, with its smooth rounded back, marked with dark spots, its white inferior surface cleft by this longitudinal denticulate aperture, and its brilliant porcellanous varnish over the whole.

Now here is evidence of change and progress again. This Cowry-sh.e.l.l is very unlike that of an Olive, with a simple spire, an oval body, a smooth thin lip, and a wide orifice; and as unlike that of a Nautilus.

Yet it has pa.s.sed through both of these stages before it was disguised as we see it now. When it escaped from the egg-sh.e.l.l, it was a minute Pteropod, with two great ciliated disks, inhabiting a transparent nautiloid sh.e.l.l, and swimming giddily about in a revolving fashion. By and by, the tiny sh.e.l.l increased, and the outer whorl lengthened, putting on a long-oval figure. Then--that is, after a considerable period occupied in increasing the dimensions of the sh.e.l.l in this form--it began to a.s.sume the adult appearance. The outer lip, which had hitherto been thin, gradually thickened and encroached upon the spire, and the mantle began to secrete and deposit on the outer surface the coat of gla.s.sy enamel.

At length the thickening of the lips proceeded to such an extent as almost to conceal the spire, and to reduce the aperture to a narrow line, the edges of which were now thickly plaited with the tooth-like ridges so characteristic of the genus. The lobes of the mantle now protrude through this aperture; and, expanding on each side, have deposited all over the exterior of the sh.e.l.l a coat of gla.s.sy enamel, studded with dark round spots or clouds, which entirely conceals the surface with the markings that were formerly visible upon it.

[Ill.u.s.tration: MUREX TENUISPINA.]

Yonder Th.o.r.n.y Woodc.o.c.k (_Murex tenuispina_) is a still more striking sh.e.l.l than either, and one whose periodic growths are peculiarly well marked. It is covered at regular intervals with rows of sh.e.l.ly spines, still longer and more numerous than those we lately admired in the _Dione_. Each series crowns a thickened ridge, which runs across the whorl, as regards the direction of its growth, but longitudinally as regards the general figure of the sh.e.l.l.

Now, the increase of the sh.e.l.l in the Univalves is performed almost exactly as in the Bivalves; namely, by the protrusion and eversion of the mantle on the existing edge. And, therefore, each of these th.o.r.n.y ridges, separated as they are by an interval of just two-thirds of a whorl, marks the termination of a new growth, the sh.e.l.ly matter rising up at the margin in this thickened ridge, which bristles with elongated points.

In this specimen we can trace ten such ridges, whence we legitimately infer ten distinct periods through which this animal has pa.s.sed, besides the nautiloid stage under which all the creatures of this Cla.s.s commence existence.

Yet, since each of these three univalves has been this day created, these inferences are deceptive. The Scorpion-sh.e.l.l was _never_ otherwise than dilated and digitated. The Cowry has _never_ had a lip that was not thickened, nor an exterior that was not porcellanous. The Woodc.o.c.k has _never_ known a moment in which its thorns were less numerous than they are now.

Notice that fine round sh.e.l.l carried along the floor of the sea, by means of a great fleshy tortoisesh.e.l.l-coloured[75] body, which, with a head of many spreading tentacles applied to the ground, crawls with a tolerably quick progress.[76] It is the Pearly Nautilus.

The amplitude of the beautiful nacreous sh.e.l.l is by no means a measure of the dimensions of the animal; for this merely sits within the shallow mouth, like a Welsh fisherman in his coracle. If we remove the creature, we shall find the cavity bounded by a pearly floor, in the centre of which is a slender tube running down from it. On breaking away this floor, we expose an empty chamber, with a similar pearly floor, through which pa.s.ses the sh.e.l.ly tube, continued through the middle of the chamber, and running down to the next. Thus we should find the whole interior of the sh.e.l.l occupied by a series of these empty chambers, fifty or upwards in number, each less than its predecessor (rather _successor_, if we regard them in the order of development), until we can trace them no longer in the minute centre of the spire.

Without dwelling on the function of these chambers, farther than to say that they appear admirably contrived to make the animal with its sh.e.l.l either heavier or lighter than the surrounding fluid, by forcing water into them through the tube, and thus condensing the contained air, or by relaxing the pressure, and allowing the elasticity of the air to exclude the water,--our business is just with the formation of the septa, as an evidence of periodic development.[77]

"The septa are formed periodically, but it must not be supposed that the sh.e.l.l-muscles ever become detached, or that the animal moves the distance of a chamber all at once. It is most likely that the _adductors_ grow only in front, and that a constant waste takes place behind, so that they are always moving onward, except when a new septum is to be formed; the _septa_ indicate periodic _rests_."[78]

These periodic alternations of rest and action, however, it is obvious, can never have really existed in an organism which has but this instant been created. The appearances, therefore, which indicate them, are illusory, considered as testimonies to actual time.

You are aware that what is often spoke of as the "bone" in this Cuttlefish (_Sepia officinalis_), is only a concealed sh.e.l.l; and I need not to dissect the animal to acquaint you that it is a highly interesting structure. A deservedly eminent physiologist shall describe it for us.

"The outer sh.e.l.ly portion of this body consists of h.o.r.n.y layers, alternating with calcified layers, in which last may be seen a hexagonal arrangement. The soft, friable substance, that occupies the hollow of this boat-shaped sh.e.l.l, is formed of a number of delicate plates, running across it from one side to the other in parallel directions, but separated by intervals several times wider than the thickness of the plates; and these intervals are in great part filled up by what appear to be fibres, or slender pillars, pa.s.sing from one plate or floor to another. A more careful examination shows, however, that instead of a large number of detached pillars, there exists a comparatively small number of very thin, sinuous laminae, which pa.s.s from one surface to the other, winding and doubling upon themselves, so that each lamina occupies a considerable s.p.a.ce. Their precise arrangement is best seen by examining the parallel plates, after the sinuous laminae have been detached from them; the lines of junction being distinctly indicated upon these. By this arrangement, each layer is most effectually supported by those with which it is connected above and below; and the sinuosity of the thin intervening laminae, answering exactly the same purpose as the "corrugation" given to iron plates for the sake of diminishing their flexibility, adds greatly to the strength of this curious texture, which is at the same time lightened by the large amount of s.p.a.ce between the parallel plates that intervenes between the sinuosities of the laminae."[79]

Now the delicately thin calcareous plates have all been formed in succession, "the first formed being at the outer part and posterior termination of the sh.e.l.l, and the succeeding new layers extending always more forwards than the edges of the old."[80] They exhibit then many hundreds of distinct deposits, each the result of a separate process, each the work of a definite period of time. The "cuttle-bone" is an autographic record, indubitably genuine, of the Cuttlefish's history.

Yes, it is certainly genuine; it is as certainly autographic: but it is _not true_. That Cuttle has been this day created.

IX.

PARALLELS AND PRECEDENTS.

(_Vertebrate Animals._)

"The organisation of the body at each epoch may be truly said to be the _resultant_ of all the material changes which it has undergone during the preceding periods."--_Dr.

Carpenter; Human Physiology_, p. 903.

The _Invertebrata_ then agree in one story, and that story is the same as what the plants had told us before. Let us try if the Vertebrate creatures bear them out.

From this promontory we can look far down into the clear profundity of the still and smooth sea. What is that large object that plays. .h.i.ther and thither yonder, now shooting ahead, now resting on his oars, now turning on his course, now cutting the surface, now descending to the depths? It is a full-grown Sword-fish, some ten feet long. We are sufficiently near him to discern that he has one short but high dorsal fin, near the head, and a minute one close to the caudal, the whole intermediate region being smooth. But this is a mark of adult age; for in early life this same species is furnished with one long and high dorsal, which is continuous from the occiput to the vicinity of the tail-fin. The remotely divided dorsal here tells of many years of life; but tells deceitfully, for the Sword-fish is but just created.

Ha! the Sword-fish has darted away, like lightning, after a finny victim. See with what doublings and windings he pursues it, and how the terrified prey uses all its powers to escape from its gigantic enemy!

Now they near the sh.o.r.e; and now the frightened quarry has leaped out of the sea upon yonder flat shelf of rock, where it lies gasping and floundering, delivered indeed from its pursuer, but only to die by being drowned _in the air_. We will descend from the cliffs, and look at it.

It is a Gilt-head (_Chrysophrys aurata_). Life is extinct now; but the brilliant colours and fine metallic reflections are scarcely dimmed--the silvery belly--the azure fins--the sides that gleam like polished steel, inlaid with bands of burnished gold!

I will pluck a scale from this brilliant silvery surface. Its hinder, or 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 mult.i.tude 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.

[Ill.u.s.tration: SCALE OF GILTHEAD.]

Every scale is therefore a doc.u.ment, on which is indelibly written the record of a mult.i.tude of processes, all effected in the past history of the fish. The successively deposited laminae are exactly a.n.a.logous to those of calcareous substance in the sh.e.l.l 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 inc.u.mbrance. It follows, therefore, that the teeth which we now see erect and threatening, are the successors of former ones that have pa.s.sed 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 pa.s.sed 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 pa.s.ses 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 dest.i.tute of lungs as it was of limbs. Any physiologist, looking at our little green Tree-frog, would p.r.o.nounce without hesitation on the stages through which it has pa.s.sed; 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 circ.u.mspectly.

It is the vibration of the h.o.r.n.y 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 h.o.r.n.y 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 acc.u.mulated.[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 ma.s.sive 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 a.s.sumed 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.

[Ill.u.s.tration: 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 pa.s.sed 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.