But there was a period in the Comatula's history when it was not a free-swimming star, but a lily-like flower of ten slender fringed petals, seated at the summit of a long stalk, with a central columnar axis of stone. Before that, the flower-head had a bud-like figure, and the petals were minute and destitute of lateral fringes; and earlier still, it was a tiny gelatinous club without any development of stone, affixed by a spreading base, and shooting forth from the top a few pellucid processes. Earlier still, it was, no doubt, an infusory-like gemmule, clothed with cilia.
Through all these successive stages, which, of course, occupied a considerable period of time, we should certainly affirm the Feather-star to have passed, did we not know that it has this very hour burst into existence.
That Panther, whose tawny fur studded with black rosettes appeared so beautiful as he bounded with agile grace from glade to glade just as we emerged from the forest, contains within his intestines, though you cannot see it, a mature Tapeworm. The body of this parasite consists of some hundreds of square flattened segments, each of which includes a complicated generative apparatus, equal to the production of thousands of fertile ova. Is not this an evidence of age? For, first of all, consider that the formation of each of these hundreds of joints has been a work of development from the anterior parts; and therefore they record as many distinct and successive processes as there are segments. And, secondly, remember that the Tænia did not commence existence as a Tænia, nor in the conditions in which it now exists, within the bowels of the Panther. It looks back to another form, and to another living nidus.
There was a time when this parasitic creature had no ribbon-like body of flattened generative segments. There was, indeed, the same curious head, a tiny globose knob at the extremity of a slender neck, furnished with the same array as now, of rows of hooks and sucking disks. But in place of the segments, the neck merged into a membranous bladder distended with clear fluid. It was not a Tænia then, but a Cysticercus.
Its home was at that time the interior of a living animal on whose vitalized juices it was sustained, but that animal was widely different from its present patron. It was an Antelope, that cropped the wiry grass and aromatic shrubs of the arid plain.
Earlier still, the germ of this Tænia was an egg lying on the ground, having been discharged from the rectum of another Panther, in the bowels of which it had been developed by one of the segments of a former Tænia.
Let us now trace the history of this organism onwards from the point at which we have arrived in our retrograde researches.
The parent Tænia, still snugly ensconced in its obscene abode, partially matured and then separated the ultimate generative segment, containing many thousands of ova, far advanced towards perfection. The detached segment now became enclosed in the fæces of the Carnivore, and was at length discharged, enveloped in the pellet. The eggs, acquiring maturity, were hatched, and the infant worms individually scattered themselves among the surrounding herbage.[66]
One of these was devoured with the herbage by a grazing Antelope, and having safely escaped the perilous ordeals of mastication and rumination, passed into the stomach of that Ruminant, whence it soon made its way by some unknown but unerring route to the liver, in the parenchyma of which organ it rapidly developed the cyst, which gave to the present stage its proper character.
The Antelope fell a prey to the ferocious Cat; its flesh was quickly digested in the stomach, but the gastric juice produced no effect on the Cysticercus. This parasite had merely changed its residence for one more commodious, or at least more suitable for its further development. It presently attached itself to the walls of the intestine by means of its oral hooks and suckers, and, getting rid of its vesicular sac, with its fluid contents, probably by absorption, it began to develop, joint by joint, that immense ribbon, which it possesses now, and which constitutes it a Tapeworm.
Such is the "strange eventful history" of this repulsive creature; a history legitimately deducible, in all its stages, from its presently-existing condition. But it is a history altogether illusory. The Tænia never was a Cysticercus: the Panther is as yet guiltless of capricide: it is this moment called into being, and the Tapeworm begins existence within it.
This lump of red sandstone that has been rolled about in the sea, till all its points and angles are worn smooth, is now roughened again by the close and firm adhesion of extraneous substance, in the form of a cluster of shelly pipes, which twine irregularly over the surface of the boulder, and then start up erect with open mouths. These are the tubes of a species of Serpula, and the worm itself is seen now slowly emerging from one of them, and introducing its conical stopper, and elegant fans of white and scarlet filaments, to the genial daylight.
Observe, however, that the tubes are not of the same diameter throughout. At the point where they start up from contact with the stone, they are considerably smaller than at the tip; and if we trace back the adherent portion along its tortuous course, we find that it constantly diminishes until it is but a slender white thread of stone. Now this slender extremity was formed first; and as the worm itself grew, so it progressively required a larger and yet a larger habitation; which was readily provided of the due dimensions, because the material, which is limestone, was secreted by the swollen collar of the worm, and being freely poured out as required, was moulded of the proper calibre by the rotatory motion of the animal, combined with the special use of certain tactile organs for the purpose.
The shelly tubes themselves afford us ocular evidence not only of their progressive formation, but also of the successive steps by which this was effected. For at certain intervals of their length we perceive rings of the common stony substance, which mark the rim or mouth of the tube as it existed after each periodic increase. The mouth of the tube is, as we see, slightly expanded in a trumpet fashion; but as the general cylindrical figure is to be maintained, the next deposit of calcareous matter is not made at the very edge of the lip, but on a ring a little way within the margin, whence it is carried up, leaving the former margin slightly projecting.
Who could hesitate to assert that a history of past time is legibly written in the annulations of these stony tubes? And yet the creatures, with their tubes, have been but this instant created.
But here is a tube of quite another construction, though inhabited by a kindred worm. It is wholly built up of sand, the inimitable architecture of the indwelling Terebella, who has thus succeeded in performing a task which defied the efforts of that too industrious artizan,—the familiar of the renowned Michael Scott.[67] Our worm has certainly spun a rope of sand, and one which holds together with surprising tenacity.
The instrument which our little architect wrought with are the long tentacles, which, like a tangled tuft of yellow sewing-cotton, twist and twine over the floors of sandy pools. Nothing at first sight seems less adequate for the purpose than those very slender, soft, and flexible threads. Dr. Williams shall tell us how they are used. "They consist of hollow flattened tubular filaments, furnished with strong muscular parietes. The band may be rolled longitudinally into a cylindrical form, so as to inclose a hollow cylindrical space, if the two edges of the band meet; or a semi-cylindrical space, if they only imperfectly meet. This inimitable mechanism enables each filament to take up and firmly grasp, at any point of its length, a molecule of sand; or, if placed in a linear series, a row of molecules. But so perfect is the disposition of the muscular fibres at the extreme free end of each filament, that it is gifted with the two-fold power of acting on the sucking and on the muscular principle. When the tentacle is about to seize an object, the extremity is drawn in, in consequence of the sudden reflux of fluid in the hollow interior; by this movement a cup-shaped cavity is formed, in which the object is securely held by atmospheric pressure; this power is, however, immediately aided by the contraction of the circular muscular fibres. Such, then, are the marvellous instruments by which these peaceful worms construct their habitations."[68]
Since the slender tentacles are the implements by which the sand-tube is thus built up, it is manifest that the existence of the tube must be subsequent to the existence of the tentacles. But the Terebella was at one time without tentacles; so that its history certainly reaches back to a date anterior to the existence of a tube. Several stages of life have intervened between that distinguished by the present worm-form, and its infant condition, when it swam as a ciliated undivided monad.
So, at least, we conclude from physiological data; but our conclusions are false, because contradicted by the fact that the mature animal with its case has been just now created.
Let us forsake the ocean-shore, and walk again through the glades of the virgin forest. A White-ant (Termes) crosses our path, and, by tracking him home, we speedily discover his dwelling, an enormous structure composed of gnawed wood cemented with an animal secretion, and formed into thin but very firm and hard layers. Swarms of labourers are passing in and out; and, on our breaking away a portion of the edifice, out come crowding the warriors, with formidable jaws extended widely, ready for the fight. In the interior we find numerous chambers stored with food, and nurseries occupied by young and eggs, the number of which is every hour increasing by the oviposition of the gravid female,—the queen of the city—who is lodged in an apartment in the very centre of the whole.
The entire edifice has been built around her; she is the hope of the colony, the only mother in this vast assemblage. It is therefore through her that we must look for a past history; and in her we find it. Some months ago, when she was not more than one thousandth part as large as she is now, though then adult, she migrated from some other city not less populous than this is now. It was just before the periodical rains, when, at the time of the great annual swarming, myriads of winged males and females were evolved from the pupa state, and flew out from their native city. This individual female was found by some of the workers that now compose this colony, and was immediately selected to be at once their prisoner and their queen.
We thus trace our great egg-laying Termes to a city of last year's building, in which for a time she was in an immature condition as a nymph, and before that passed a still less-developed stage as a larva. Hence her life-history goes yet farther back to an egg, originally laid by a former female in exactly the same circumstances as those in which we find this guarded and immured individual.
Thus we reason; but the female, with her host of attendants, and the house, which is inseparable from their present stage of existence, has been created to-day.
See that creature which with loud ringing hum is whirling round and round the tassel-like blossoms of this noble Eugenia. You would think it a bird from its massive size, but it flashes and sparkles in the sun, like a great jewel. Now it suddenly alights on one of the crimson flowers, and you may perceive that it is a beetle;—a beetle of vast size, and glittering like a lump of burnished metal;—it bears the name of Goliath,—a giant clad in polished armour.
This is his first hour of existence; now for the first time has his nervous system responded to the stimulus of the sweet air and genial sunshine. An hour ago he had no nervous system; no system of any sort; no life; no being; no anything;—he was not until this hour.
Yet if we were to ask a friend conversant with entomology his opinion on the age of this insect, he would immediately give it; not, however, as an opinion, for he would repudiate the uncertainty which such a word implies, but as an indubitable fact, resting on the infallible grounds of constant observation and undeviating experience.
"This fine Goliathus," he would say, "has not long, probably, emerged from a hollow case of oval form, made of particles of earth agglutinated together by a secretion from the mouth of the larva, and concealed under the surface of the ground. Within that sepulchre it has left its cerements,—the shrivelled skin of the pupa, in which it had been wrapped up motionless like a mummy, for several weeks prior to its appearance as a glittering beetle. The construction of the oval cell was the last act of the larva, a thick, massy, heavy-bodied grub, which had fattened for years by feeding on the roots of plants beneath the soil. Four years passed away[69] while yon beetle lay on its side, darkly labouring at this occupation; and before that it was a minute egg for some weeks. The specimen before us cannot be far short of five years old."
No such thing: the witness is at fault: the Goliathus is not an hour old.
Take notice of the swarm of Gnats, which, like a dim cloud, are uniting in choral dance and song in the beam of the setting sun. Every member of the band that "winds his shrill horn," has had an aquatic before he had an aërial existence. A week was spent, in lobster-shape, with two breathing tubes on the summit of his body, in passing alternately from the bottom to the top of yonder stagnant pool, and then back from the top to the bottom. And a month was occupied in pretty nearly the same employment, but in another mask,—in fish-like form, with the star-tipped breathing-tube projecting from the side of the tail. But for some months earlier still it was a little lenticular egg, which was agglutinated with a number of others into an oval concave boat, that floated to and fro on the surface of the pool.
And there was something worth observing in that tiny skiff of eggs; for it did, in its artful construction, carry the evidence of time back to a former generation. The eggs individually and separately would have sunk to the bottom of the water; it was, however, essential to their life that they should be in contact with the air as well as with the water. Hence they were so arranged in the aggregate, that the mass should swim, though the constituent individuals could not. To effect this, the parent Gnat, resting on the calm surface of the pool, crossed her two hind legs, and laid an egg perpendicularly in the angle so made: others were added in succession, all maintaining the perpendicular position, all glued together by a cement that resists water, but so arranged, the crossed legs being still the mould, that the outline should be spindle-shaped, while the summits of the central eggs, being a little lower than those of the outer ones, gave a concavity to the boat. So buoyant was it when finished, and the mother's legs withdrawn, that even a drop of water falling full upon it from above, would have failed to submerge it. There it floated, week after week, and month after month, all through the winter, till the genial sun of spring hatched the fish-like larvæ to begin their wriggling existence beneath the surface.
Now may we not say with confidence, that the sounding-winged insect looks back to the pupa, the pupa to the larva, the larva to the egg-boat? And more, that the form of the boat,—a form so essential that it could not have lived without it,—looked back to the crossed feet of the mother-gnat, the impress of whose angle its extremities sustained?
Of course we might reason thus: but yet we should be at fault; for the ringing swarm of merry Gnats has been this very evening created.
The Case-flies (Phryganea) that look like delicate moths of sober-brown hue, flitting over the surface of the pond, have, like the Gnats, spent a considerable time under water. When they were larvæ, they industriously collected small shells, fragments of stone, bits of reed, and the like matters, and, connecting them together with strong silk, made out of them slender tubes, in which they sheltered their soft bodies from harm, while their hard polished heads and shoulders projected from the open end. And after having lived through the winter (at least, but I rather think more than one winter) in this state, each closed up the entrance of his castle, by spinning across its open end, a transverse screen of lattice-work, made of very strong and stout silk, which, while it should serve the purpose of keeping out evil-minded intruders, during the helpless inaction of the pupa, should at the same time admit the free ingress and egress of water necessary for its respiration.
The life of the larva, and the exercise of these, its curious instincts, are, together with the duration of the pupa stage, inseparable precedents of the imago state in which we now observe the flying insects. No, not "inseparable;" for in this case, at least, they had no existence in time; they are prochronic developments.
In this pond at our feet there is an object worthy of a moment's observation, minute though it is, for it is only visible as a speck to the unassisted eye. On one of the whorl-filaments of this tuft of Myriophyllum, there stands up a cylindrical tube, firmly adherent to the plant by its foot, but free at its upper end. Small as it is, this chimney is built up of hundreds of pellets, solid, round, and yellow; placed in symmetrical order, and firmly cemented together. What has made this tube? Ha! here is the little architect ready to answer for himself; he thrusts out his head and shoulders from his chimney-top, and announces his scientific cognomen as Melicerta ringens.
Look! he is in the very act of building now. Did you see him suddenly bow down his head and lay a brick on the top of the last course? And now he is busy making another brick; his mould is a tiny cup-shaped cavity just below his chin; his material the floating floccose atoms of vegetable refuse. Cilia along his flower-like face collect these atoms into a stream, and pour them into the cup; and cilia within the cup whirl them rapidly round and round in many rotations, until with the aid of mucus they are somewhat consolidated into a round pellet. The brick is made, and nothing remains but that it be deposited next the former, in regular progression, and this is done by the tiny τεκτων, suddenly bending his head forward, and bringing the chin-cup with exact precision to the spot.
And how long has he been engaged in this piece of work? Little more than a day. It was commenced yesterday, when the creature was not more than one-third as large as he is now. But he had lived a few hours before the commencement of his work. He was a rover before he began to be a house-keeper. In that early stage of youth and freedom, before he had made up his mind to settle in life, he had no chin-cup, no flower-like face, and of course no tube. A cylindrical gelatinous pellucid worm, he issued out of the egg, with a brush of cilia on his crown, and danced waywardly through the water. While thus occupied, his form underwent some preliminary modifications, and at length was sufficiently matured, to enable him to choose a spot for the passing of his future life, and to commence the building on which he is still engaged.
Not so. The pellet which he deposited when we began to look at him, was the first he had ever made; he had been created but that moment; and all the previous pellets of the case had been called into being just as we saw them. They were built up prochronically.
I tear a piece of bark from the trunk of this half-decayed tree, and have disclosed amidst the rank-smelling damp and rotten wood, a large Julus, a slow-moving creature, with some hundred-and-fifty little twinkling feet. As this specimen has attained its adult condition, it must be at least two years old; for it does not acquire its reproductive organs and perfect development till that age.[70]
This creature has passed through a rather curious history of evolutions. The egg from which it was produced was lodged in a chamber excavated by the parent, a few inches below the surface of the rotten mould. From this egg proceeded a little kidney-shaped body, without limbs or motion, completely enveloped in a swathe of delicate transparent membrane. About a fortnight it remained in this helpless state, during which its organs had been forming out of the constituent cells, by repeated subdivision, and definite arrangement. At length it burst its cerement, and a minute Julus appeared, not more than 1/200th of an inch in length, composed of a head with antennæ, and a body of eight segments, of which the first three carried each a pair of legs.
All the multitudinous limbs which we see in this adult have been produced in successive moultings, and all the numerous segments have been produced by the subdivision of the last but one,—that is the joint preceding the anal one,—six at a time.
By the time the little animal was ready for the second sloughing, that is, in about a week after the preceding, three more pairs of feet were seen, which had budded from the fourth, fifth, and sixth segments, but which were as yet closely packed down beneath the investing skin; the seventh segment also was obscurely marked into six divisions. The skin was now thrown off, and these changes were perfected; the little Julus now had six pairs of feet, and thirteen segments.
This process was repeated again and again; the new limbs always developing on the segments last produced, and six new segments being always formed out of the existing penultimate. And by this gradual succession of development, the animal has attained the number of limbs and segments which we now perceive. The antennæ and the eyes have likewise passed through successive stages.
We have a right to infer the lapse of a period sufficient to produce these changes, for we see their indubitable results; but our inference would only lead us astray, because we have not allowed for a disturbing influence,—that of the Law of Creation. This is the Julus's first hour of life.
See, on the trunk of that towering Cedrela, a round hole, out of which a large Beetle is in the act of emerging. It is a noble Buprestis, encased in glittering mail, of the most refulgent metallic splendour, crimson, gold, and green. Can we find any clue to his age? Yes: the white grab has rioted and fattened in its burrows in the timber of this tree for many years; ever gnawing away with its horny auger-like jaws the solid wood in tortuous galleries, which constantly enlarged, as it progressively grew, while its wake, as it advanced, was partially filled by its ordure. The old tree is, no doubt, perforated, through and through, by its winding corridors, as large as your middle finger. As soon as the vermin had passed this his nonage, which, as I say, may have occupied a dozen years at least,[71] he sank into his short pupa-sleep, and here we see him paying his first visit to the light of day.
True; this is his first experience of daylight, and indeed of anything; for all the pupa-sleep and the larva-labour were prochronic in this case. The Beetle is just created.
Hark to that hollow roar! There is no mistaking that majestic sound. It is the voice of the many-sounding sea. Yonder through the trees we catch a glimpse of its shining face, and here we are at the verge of the cliffs, against whose feet the waves are breaking in white foam. We will clamber down to the rocks.
In this weed-fringed tide-pool there is a fine specimen of the Shore-crab (Carcinus mœnas). It is a male just arrived at the perfection of adult age; its carapace smooth and wholly dark-green in hue, its under parts rufous orange. Its claws. are large and sharp; and the promptitude with which it presents these formidable weapons, extended to the utmost, shows how conscious it is of its warlike powers.
To all appearance this Crab is several years old;[72] I mean in this his present perfect or imago form. When this form was first assumed, the diameter of the carapace was not more than an eighth of an inch; it is now two inches; a great many periodical sloughings of the crust must have occurred to accomplish this sixteen-fold increase.
But four distinct metamorphoses were passed before the commencement of this form. There was the Grapsoid form with the outline of the carapace nearly parallel-sided, and the dentations on the sides. Before this there was the Megalopa form, with the carapace ovate, and the abdomen projecting behind. Before this there was the Zoea form, with the carapace rising into a tall erect spine, sessile eyes, no claws, and the abdomen a slender jointed cord ending in a triangular plate. And before this, there was the egg, which was laid by the mother Crab, and carried by her for a considerable time attached to the false feet of her abdomen.
All these evidences of age, clear and unanswerable though they are, are yet fallacious, because the Crab has been created but this morning.
On this sea-washed branch of a tree, which has been blown off by some tempest, and carried into the ocean, there is a single Barnacle (Lepas). It consists of a hand of many pairs of fringed fingers, protected by a shell of five pieces, and a long flexible cartilaginous stalk, by the lower extremity of which it adheres to the timber.
The shelly valves are all crossed by strongly marked lines running over their surfaces in a direction parallel with each other, and with the outer margins of each valve. These, like the corresponding foliations in the tube of the Serpula, indicate the successive stages of growth; the outlines of every valve having stood at each of these growth lines in succession. On each of the scutal valves in this individual I can count about 260 growth-lines: if we suppose one of these to be made in a week,[73] and the increase to proceed uniformly throughout the year, we must conclude the valve to have been just five years in making.
This animal, like others we have already examined, had, moreover, a history before the first vestige of a valve was formed. It had passed through several metamorphoses; in its pupa stage it had the form of a Cypris, and in this condition it first became adherent to the timber: before this it was a larva, having a general resemblance to another Waterflea, the Cyclops, especially in its younger stages: in this state it moulted several times. Nor was this the beginning of its life; for there was the still earlier condition common to all these classes of animals, viz. that of the egg, which was laid and carried for some time by the parent Barnacle, and at length hatched while within the valves of her shell.
Thus, through a course of several years we are able to trace back the existence of this Cirriped, to its parent of a former generation. But our conclusions are altogether vitiated by the simple fact that this individual is the first of its species; it never had a parent; it never was an egg.
From the rocky pool before us I have picked up a rough pebble, the surface of which is incrusted with a delicate work of stony lace. This fabric, too fine to be resolved by the unassisted eye, consists of the oval cells of a species of Lepralia. There are some hundreds of cells in this patch, which altogether does not cover a square inch of the pebble; and they are all made after one pattern, and set in a very regular manner, in quincunx. Each is a minute slipper-shaped box of stone, with the orifice set round with spines for the protection of the inmate, a transparent, elegant, and sensitive Polypide, which bears on its head a coronet of ciliated tentacles.
I am not going to describe the interesting structure and economy of this atom of life; but merely wish to direct your attention to one point,—the evidence which it affords of the lapse of past time.
Every one of these hundreds of stony cells, together with its living tenant, was normally produced by a process of gemmation; each having budded forth from the side of its predecessor as a knob of clear gelatinous flesh, in the midst of which was developed, first the cell, and then the polypide,—the latter appearing in a rudimentary condition, and gradually acquiring its proper organs, before the orifice of the cell was opened.
I said every one of the cells was thus formed; but I ought to have excepted a single cell, which, though in nowise differing from the rest in form or structure, had a very different origin. This was the primal cell, and its beginning was as follows:
A minute atom of a scarlet hue, and of a semi-elliptical shape, was one day whirling round and round with rapid gyrations in the open sea. It was of soft consistence, covered with strongly vibrating cilia, and furnished with some stouter setæ. After enjoying its motile instincts awhile, it settled down on this pebble, and became stationary. Presently it secreted and deposited calcareous matter around at, like a coating of the thinnest glass, the red parenchyma receding from the hyaline wall towards the centre.
Soon an orifice with thickened edges appeared on the upper side, and minute spines grew from the edges, which quickly lengthened. It was now a Lepralia cell, and now the polypide was developed, and protruded its mouth from the orifice, surrounded by its elegant bell of ciliate tentacles. This solitary cell became the parent of hundreds more, by the gemmative process which I have already described.
But the red swimming atom;—whence came that? Well, it was shot out from the interior of a previous Lepralia, the result not of a gemmative but of a generative act. It originated in another patch similar to the one which incrusts this pebble, and that, in like manner, and by exactly similar stages, looked back to an anterior patch, and so on.
Plausible as this inference is, it is false; for the little aggregation of cells and polypides has been called into existence by the Divine fiat, this very instant.
We are still at the sea-shore. Within the long and narrow crevices into which these low-lying ledges of shale are split, innumerable tufts of sea-weed,—olive, purple, and green,—are perpetually waving in the wash of the sea. On one of these branching shrubs of Phyllophora, there is adhering, apparently cast there by accident, an irregular mass of pellucid jelly. It firmly cleaves to the alga, enclosing the bases of several branches within its firm but gelatinous substance.
This knob of jelly is a compound animal of the genus Botryllus, and it has just been created as we see it. In order to understand its nature, look at it more closely.
Enclosed in the clear purplish-grey jelly, in the midst of scattered lighter specks, we see several star-like figures of bright hues, in which yellow and red are predominant; the symmetrical arrangement of which pleases the eye, and reminds us of some ornamental pattern designed by human art. Each star is composed of several (three, seven, ten or more) pear-shaped animals, with their smaller ends meeting in the centre around a common orifice, from which a current of water is discharged.
Now this assemblage of animals bears evidence of progressive development. Some time ago a tiny egg was discharged from a parent Botryllus, which presently produced a little active tadpole-like larva, called a "spinule." This swam actively by means of its wriggling tail; but at length it settled head downward on this piece of sea-weed. Immediately the head adhered, by an effused cement, to its support; the tail now gradually disappeared; and the round head, in the midst of a mass of jelly-like cement, began to display two orifices on its surface. It soon assumed a pear-like shape, and thus the first Botryllus was formed.
From the side of this "pear," another was developed by gemmation, and a third on the opposite side; the smaller ends of all were in contact, and the orifices of these extremities began to merge into one; while the large ends diverged. A fourth and a fifth "pear" were successively produced in the same mode, until a star or "system" was formed. Meanwhile the surrounding mass of living jelly had been commensurately enlarging, and a new Botryllus, separate from the other star, had been produced in the jelly, which was the commencing point of a second system; and thus, by degrees, the compound mass of systems has grown to its present state of development.
This process has been one of time: the adhesion of the "spinule" took place in about sixteen hours after its escape from the egg. The appearance of the two orifices was when the little animal was four days old; and by the end of a week a second "pear" had budded. The attainment of the present condition may have occupied about six months.
Nay; time has been no element in this development; it is prochronic development; it is the development of creation, not of nature.
Behold that ruffling of the smooth surface of the water; it is caused evidently by the forcible ejection of a current from some source a little way beneath the surface. Yes, it proceeds from the orifice in this mass of calcareous grit; where the protruding pipe of shell indicates the snug fortress of a Clavagella. I will carefully break away a little of the soft stone, and we shall see the curious structure more clearly. Ha! I have split off a piece which nicely exposes the whole burrow, without having materially injured the creature or his shell.
You see it is a bivalve Mollusk with one valve firmly imbedded and cemented into the stony wall of its chamber. But the hinder end of this valve is continued into a shelly tube, intended to protect the siphons, which is carried through the gallery forming the entrance into the chamber, and opens by a wide orifice in the free water outside. It is to this tube that I call your attention.
You observe that on its outer surface there are several foliated expansions of the shelly substance, surrounding it like so many frills at pretty regular intervals. Each of these foliations is a permanent record of a certain epoch. The terminal one is the margin of the tube-wall everted. The one below this was at some past period the eversion of the margin at what was at that time the extremity. The third frill had in like manner terminated the tube still earlier; and so with the fourth and fifth. It is impossible to look at these expansions, and not to believe that they have been formed in succession, in this way, by the periodic growth of the tube.
There was a time when, the first frill was not commenced; when the creature was a Mollusk with simple valves. But even this was not the beginning of its history. It was as a swimming Infusory with a broad ciliated disk, and a lashing flagellum, that the creature commenced its independent career; and it was doubtless in this condition[74] that it found its way into the burrow of some Saxicava. Here its tiny transparent valves were secreted; the left valve was soon cemented to the chamber; and then the creature began to secrete and form the tube around its siphons, which was progressively enlarged, and adorned at every stage of elongation by these witnessing frills—whose testimony is recorded in imperishable stone.
What can be more irresistible than such evidence as this? And yet we must take exception to it on the ground that this is the very hour of the animal's creation.
The elegant spinous shell-fish that we discern yonder, half-buried in the sandy floor of the sea—I mean that lilac-tinted Prickly Venus (Dione Veneris) needs no shelly protection for its siphons, which, as you may observe, are protruded to a great length. But a lesson not less instructive than that taught by the tube-frills of the Clavagella, is inculcated by the valves of the Dione. Near the hinder margin of each valve there is a ridge which runs from the beak to the front edge, a ridge which bears the series of long slender shelly spines, that imparts such a charm to this shell.
Each of these spines records an interval in the growth of the shell. There are sixteen distinctly enumerable; each of which may possibly mark a year's growth. The increase of bivalves, however, is slow; and it may be that a longer interval than a year has intervened between spine and spine. For if we look more closely at this beautiful shell, we see that the whole exterior of both valves is marked with concentric foliated ridges, which are also indubitable lines of growth; and that these are twice or thrice as numerous as the spines, from one to five being intercalated between those which support the prolongations of the shelly substance.
Each of these concentric lines has a history. Every line, as well as every spine, has been produced by a protrusion and eversion of the glanduligerous edge of the mantle, which then secreted and poured out a copious deposit of calcareous matter along the margin of the previously existing valve. In this species each periodic deposit took the form of a ridge slightly elevated above the general surface; and, because the turned up margin of the mantle invested the edge of the valve already formed, therefore the new layer, with its elevated ridge, was concentric with the last edge, which was concentric with the previous one, and so on, the common centre of all being the beak (umbo) at the back of the valve.
The spines were formed in a manner essentially similar. At every second or third period of increase, the margin of the mantle, which is very versatile and protrusile, was thrust out, at the point which corresponds to the spines, into a long fleshy groove, by the reduplication of its edge. Within this groove the calcareous secretion was poured out; and after it had been allowed a few moments to harden or "set," the mantle-groove was cautiously withdrawn, and a new spine was exposed, as a produced end to the foliated ridge.
Yet, though this is the normal and natural mode of production, both of the concentric line and of the spines, it would be illusory to conclude that they have been so produced in the present example. The entire formation of the Dione before us has been ab-normal and preter-natural: it has been created, not born: the whole development so legibly written on the shell has been prochronic.
There goes the Scorpion Stromb (Pteroceras scorpio), crawling over the rocks with protruded head and tentacles, and bearing his massive house on his back. This shelly house of his will afford us a good example of structural development.
The great dilated lip, and the long finger-like processes of its edge, had no existence in the youthful days of the shell; they are marks of adult age: when young, the shell 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 (Cypræa tigris). Its shell 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 space three or four times as large as the shell. 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 shell, 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 shell, 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-shell 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 passed through both of these stages before it was disguised as we see it now. When it escaped from the egg-shell, it was a minute Pteropod, with two great ciliated disks, inhabiting a transparent nautiloid shell, and swimming giddily about in a revolving fashion. By and by, the tiny shell 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 shell in this form—it began to assume 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 glassy 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 shell a coat of glassy enamel, studded with dark round spots or clouds, which entirely conceals the surface with the markings that were formerly visible upon it.