Part 12

Who, on looking at these two creatures side by side,--the Sea-Urchin and the Encrinite,--would imagine that they possessed any close natural relationship, or would suspect that they could have been framed on the same model? Yet it is really so; there is a common plan of structure in both; pervading, too, many intermediate forms, which at first sight would seem to manifest as little resemblance to the one as to the other. It would, in fact, be easy to select from any well-furnished museum a continuous chain of specimens, whose links approach each other so closely as to form an unbroken series from the Urchin to the Feather-star.

CONNECTING LINKS.

Among the Urchins proper there are some species, such as the Sphere Sea-egg, and the one known as Fleming’s, which have a figure not far from that of a globe. Others are much more depressed, of which the little Purple-tipped is a notable example. Still the spherical shape is conspicuous. From this rounded form other species, more and more flattened, gradually lead to the _Scutella_, which takes the form of a thin round plate, quite flat beneath, but slightly convex on the upper surface. The structure is the same as before, but the spines appear to the naked eye only as very minute hairs; but, when magnified, are found to be of the most elaborate workmanship, each having a movable socket-joint. In the genus _Clypeaster_, the round outline is changed for a five-sided figure, the angles of which in succeeding species project more and more, and the spaces between become more and more indented, till we arrive at the Starlets, and at length to the Cross-fishes (_Asteriadæ_). The rays gradually becoming longer and more slender, we are brought to those in which they are so lengthened as to resemble the tails of so many serpents, whence they are named _Ophiura_. In succeeding genera, such as that called Medusa’s head (_Gorgonocephalus_), the central part is still further diminished, and the rays are divided into branches of great length and number. Each ray, soon after its commencement, separates into two more; these again into two others, and so on to an astonishing extent. Upwards of 2500 ramifications have been counted on a single specimen, presenting a living net, by the contraction of which any small animal once touched would inevitably be detained. The sucker-feet are no longer found, these animals changing their position by dragging themselves along by their flexible arms. Finally, we have the Feather-stars, which, as we have seen, in their infant condition, and the Lily-stars, which throughout life (as the abundant fossil species in our own land, and that noble one which still exists in the West Indian seas), consist of slender-jointed arms, with feather-like filaments, seated at the free extremity of a tall jointed stalk, also furnished with whorls of filaments, which is fixed by its base to the solid rock.

Altogether, the series presents us with one of the most instructive and most marvellous examples of the vast variety of external form and internal structure which may be assumed by almost insensible modifications of one plan of organization; and so of the unfathomable resources of wisdom in the ever-blessed God. For every one of these links,--and there are multitudes which I have not named, found either in remote seas or in a fossil condition, that fill up the gaps with close gradations--displays an essentially common model; and the least fragment of the stony skeleton of any one would be sufficient to enable a competent naturalist to decide authoritatively, the instant he looked at it beneath his microscope, that it belonged to the great class ECHINODERMATA. The calcareous shell of which the framework is composed,--a glass made of lime,--is deposited in a fashion which, while common to all, is found nowhere else throughout the whole animal kingdom.

FLAT-CRABS.

Let us turn from these investigations, fascinating as they are, to examine the ways and means of two or three other creatures, familiar enough to us who habitually explore the sea-margin. I allude to certain members of the great class CRUSTACEA, not Crabs nor Lobsters exactly, but called so by courtesy, something in fact between both. My dredger’s hauls are always sure to contain, creeping in the tangled thickets of _Laomedea_, _Antennularia_, and other of the flexible Polyps, or playing at bo-peep from the interstices of the _Serpula_ masses,--numerous specimens of a tiny Crab,[91] with a circular flat shell, no bigger than a split-pea, large wide claws, and very long antennæ, like two hairs. They are of various colours, sometimes pure white, sometimes chocolate-brown, and often clouded with different hues. Minute as they are, they are not despised by great fishes; for the heavy-sided, clumsy-headed cods, that occupy so large an area on the fishmonger’s slab, are often found to have their stomachs packed full with these little Crabs; which doubtless the glutton picks off one by one, enjoying the taste of the savoury atom as it rolls over his fat fleshy tongue.

THEIR MANNERS.

But we may much more easily procure specimens of his bigger brother, the Shaggy Flat-crab,[92] which abounds under nearly every flat stone at low-water on Babbicombe beach, and indeed almost everywhere else, under the like conditions. He is a curious subject, though far from attractive as to his _personnel_, for he is, I regret to say, of irreclaimably dirty habits. You never find him but he is begrimed and saturated, so to speak, with the impalpable red mud of which our soil consists,--the _débris_ of the red sandstone. Yet blame him not. He is more hirsute than a modern swell; his hands and his face are as hairy as Esau’s; a dense short pile of stiff bristles stands out from all his prominences, and catches and entangles the sediment in the midst of which he loves to riot. I say again, blame him not; we must not infer that he likes dirt for its own sake, because he gets his living in it, any more than the sweep or the dustman chose his trade because he had a _penchant_ for the grime. Nay, dirty as our little flat friend is, he is endowed with organs expressly for the purpose of cleaning himself, and fails not to use them too. On first looking at him you would suppose, comparing him with other Crabs, that he was short of one pair of feet; yet presently, from a narrow, almost invisible crevice behind, he jerks out two jointed limbs, as slender as bristles, which, however, are each terminated by a tiny two-fingered claw, and are beset throughout their length by stiff short hairs standing out at right angles, like a brush. These feeble limbs are indeed cleansing brushes, with which he keeps certain portions of his person clean, applying them with the greatest ease to the whole surface of the abdomen, and under-side of the carapace or body-shell, while the delicate fingers of the little hand are used to pick off adhering matters that cannot be removed by brushing. Then having done his washing, he cleans his brushes with his mouth, and snugly folds them up, and packs them away in their groove till he wants them again. Yet with all this, he remains, as I said at first, a dirty subject notwithstanding.

A curious chapter in the history of this little creature, which I have put on record elsewhere,[93] is, I think, so very instructive, that I may venture to repeat some parts of it here. Let me premise that the Crab habitually lives under stones, a habit for which the remarkable flatness and thinness of all its parts adapts it; he has somewhat of the appearance of having been crushed flat by the pressure of the stone under which he lives. He does not wander much to seek his food, but expects it to be brought to him, he making provision for its conveyance.

FOOD-GATHERING ORGANS.

The organs which he employs for this end are the outer foot-jaws or pedipalps, which are of unusual length, and are fringed with incurving hairs. Watching a Flat-crab beneath a stone close to the side of my tank, I noticed that his long antennæ were continually flirted about; these are doubtless sensitive organs of touch, or some analogous sense, which inform the animal of the presence, and perhaps of the nature, of objects within reach. At the same time I remarked that the outer foot-jaws were employed alternately in making casts; being thrown out deliberately, but without intermission, and drawn in, exactly in the manner of the fringed hand of a barnacle, of which both the organ and the action strongly reminded me. I looked at this more closely with the aid of a lens; each foot-jaw formed a perfect spoon of hairs, which at every cast expanded, and partly closed. That this may be better understood, I may say that the foot-jaw resembles a sickle in form, being composed of five joints, of which the last four are curved like the blade of that implement. Each of these joints is set along its inner edge with a row of parallel bristles, of which those of the last joint arch out in a semicircle, continuing the curve of the limb; the rest of the bristles are curved parallel or concentrical with these, but diminish in length as they recede downwards. It will be seen, therefore, that when the joints of the foot-jaw are thrown out, approaching to a straight line, the curved hairs are made to diverge; but as the cast is made, they resume their parallelism, and sweep-in, as with a net, the atoms of the embraced water. The microscope revealed to me a still higher perfection in this admirable contrivance. I then saw that every individual bristle is set on each side with a row of short stiff hairs, projecting nearly at right angles to its length; these hairs meeting point to point those of the next bristle, and so on in succession, there is formed a most complete net of regular meshes, which must enclose and capture every tiny insect or animalcule that floats within its range; while, at each out-cast, it opens at every mesh, and allows all refuse to be washed away or fall to the ground. For we are not to suppose that the captures thus promiscuously made are as indiscriminately swallowed. A multitude of atoms are gathered, which would be quite unfit for food; and a power of selection resides in the mouth, whether it be the sense of taste or touch; or any other analogous but recondite perception, by which the useful only is admitted, the worthless, or at least the injurious, being rejected.

SQUAT-LOBSTERS.

Companions of the Flat-crabs, closely allied to them in all essentials of form and structure, yet widely separated by general figure and appearance, and to some extent by habits too, are the Squat-lobsters. They, too, are somewhat flat, but they are more decidedly lobster-like, with a distinctly jointed abdomen as broad as the body, terminating in wide and strong swimming-plates. This portion is, during rest, thrown-in under the body, much more completely than a true lobster or prawn can do it, and yet is by no means so permanently set in that position as in the true crabs. The Flat-crabs and the Squat-lobsters constitute an intermediate group between the short-tailed and the long-tailed Crustacea, the Flat-crabs inclining to the one, the Squats to the other alliance. When the abdomen is wrapped-in, the outline of the Squat is nearly oval, particularly in the commonest species, the Olive or Scaly Squat.[94] That of the Scarlet or Embleton’s species[95] is a longer ellipse. The front runs out into several sharp spines, as do also the edges of the carapace; and the inner edges of the front limbs, which carry long and stout claws, are very spiny. More formidably armed in this respect, however, than either, is another species, found occasionally at low-water, the Painted or Spinous Squat,[96] all the limbs being set, on both edges, with stout sharp prickles. The last named is the largest kind, being sometimes four inches long; then the Olive, which is commonly from two to two and a half; while the Scarlet rarely exceeds an inch and a half. They differ very much in colour, the Olive being of a dull blackish green, with narrow transverse lines of pale yellowish; the Painted somewhat of the same general hue, but with the eyes and the tips of the claws of the most vivid scarlet, while the body is varied with lines and spots of an equally brilliant azure. Embleton’s is of a more or less bright red, varying from a light orange or warm cream colour to a full orange, clouded with patches of deep scarlet. The last is an inhabitant of deep water, obtained only by the dredge; by this means, however, I obtain it in considerable numbers. The other two are found, the first abundantly, the second rather rarely, under stones in our coves. I have found, in autumn, in such situations, several specimens of small size, rather smaller than full-grown Embletons, which I conclude to be the young of the Painted. The whole body is pale blue, tesselated all over with black and reddish brown; the legs are banded with red, and the hands are of the same colour. They have a very pretty appearance.

The whole race are very cautious and timid. With the long claws, and the longer antennæ, stretched out to their utmost in front, the suspicious Squat feels the unknown ground with delicate touches; should he touch any object that moves, he gives on the instant a vigorous flap with the broad incurved tail, and shoots backward through the water to the distance of several inches. At the same moment all the legs are thrown forward in the line of the body, to diminish the resistance. Mr. Couch says: “It is very remarkable to witness the accuracy with which they” [he is speaking of the Painted species specially] “will dart backward _for several feet_ into a hole very little larger than themselves: this I have often seen them do, and always with precision.” This would surely be a remarkable feat for an animal in the air; how much more through a medium so dense and resisting as sea-water!

I have elsewhere[97] described and figured the young of a species of this genus in two of its stages. In the first it may be compared with a prawn, having a lengthened slender body, whose fore part is protected by a prawn-like transparent carapace, with an immensely long straight spine in front, and two hooked ones behind. In the next stage the general figure is acquired, but still the form is more like that of _Porcellana_ than of _Galathea_.

FOOTNOTES:

[86] _Lepidogaster bimaculatus_, of which individuals of different varieties of colour, and in different attitudes, are represented in Plate XIX.

[87] Let me refer my readers to an excellent and most interesting paper on this little fish, by my friend, Mr. W. R. Hughes, in the _Zoologist_ for July 1864.

[88] _Asterina gibbosa_, figured in the right-hand foreground of Plate XX.

[89] _Echinus miliaris_, a specimen of which may be seen delineated in Plate XX., in the upper left-hand corner.

[90] _Comatula rosacea_; a fine specimen of which, taken by myself in a little cove near Torquay, I have delineated in the centre of Plate XX.

[91] _Porcellana longicornis._

[92] _Porcellana platycheles_, represented by the central figure in Plate XXI.

[93] _The Aquarium_: 2d Ed. pp. 37-45.

[94] _Galathea squamifera_, represented in Plate XXI., at the left hand, in the act of shooting backward.

[95] _G. nexa_, for which see the right-hand corner of the same Plate.

[96] _G. strigosa._

[97] _Tenby_, p. 169, Plates VII. and VIII.

VIII.

AUGUST.

What eager pursuer of marine animals has not gloated over a rock-pool? On all our rocky coasts we find them more or less developed; but it is on these south-western shores, where the compact limestone juts out into promontories, that we find them in perfection. The burrowing mollusca specially favour the limestone; the _Saxicava_, I think, lives in no other medium; and it is to the operation of this coarse ugly little shell-fish that this rock is indebted for the honeycomb-like excavation which has eroded its surface. Below a few inches this erosion does not extend, for the _Saxicava_ is but a small animal, and its siphons must reach the orifice of its burrow; therefore it never goes deeper into the stone than will allow it comfortably to bathe its red nose in the free water, though it is not at all particular about the angle to the surface at which it bores. The myriads and myriads of these auger-holes that have been bored remain, though the feeble animals perish generation after generation; each new-born shell-fish makes a new bore for itself, never appropriating one ready-made, and so there is a perpetual excavation of the living rock with these shallow auger-holes, always of the same width, or nearly; about half-an-inch. The result is what we see; that the surface of the rock knows no such thing as a plane surface, but a surface covered with smooth borings, running in all directions, so as continually to break in on one another; and that so close together, that the interspaces form narrow knife-edges, and sharp angles and projecting points. A particularly interesting circumstance is, that this honeycombed condition is characteristic not only of that level of the rock which is covered by the sea for some portion of every tide, but of that part, to a certain height, which is never covered at all. The Mollusca, it is true, cannot live wholly deprived of sea-water, and, in fact, there are none in this ever-dry portion, though the burrows by thousands testify that they were there once. We must infer that the coast has been generally elevated; perhaps by slow and imperceptible degrees, by an operation still proceeding but unappreciated; perhaps by some sudden convulsion which took place at a remote era, unrecorded and forgotten.

HOW ARE ROCK-POOLS MADE?

When once raised beyond the level of the highest tide, the eroded surface appears to have a permanency which defies the action of the elements for an undefinable period; for it seems liable to little change. It is probably comparatively unalterable, or alterable slowly, beneath the level of the lowest tide. But between tide-marks, the perpetual change from wetness to dryness and back again, and the incessant wash of the waves, which frequently beat and dash upon the eroded surface with immense violence, are continually grinding down the projecting points and thin walls of stone, and thus creating a new surface, to be bored afresh by new generations of Mollusca.

It has seemed to me that these burrows have played and are playing an important part in the formation of the numberless rocky basins which we call tide-pools, and in which we marine naturalists so much delight. Let us look at the process. About half-tide level there is a mass of bored rock, from whose burrows the tenants are dying out for want of sufficiently long water-covering. A heavy sea is breaking over it, which has snapped off the thin partition beneath two contiguous burrows, breaking it into several sharply angular bits, which fall into the hole. The whirling and eddying of the waves rattle and roll these fragments round and round day after day, week after week, till at last they are ground to nothing: but an equal effect has been produced on the hollow which held them; its cavity has been widened and deepened by the same grinding action. By-and-by a pebble is rolled in, and being almost large enough to fill the cavity, it does not readily wash out, but grinds round and round with the motion of the sea. So the process goes on, perhaps for centuries, perhaps with long intervals of almost sameness; every stone that is washed-in enlarging the work; while, when once the hollow has become only ever so little larger or deeper than those which surround it, the pebbles will have an increasing tendency to roll in and to stay there. So, at length, the basin is formed, tiny at first;--I know scores not so big as a slop-bowl, which yet have their furniture of elegant little sea-weeds, green and purple, and their tenants of worms, and shrimps, and polyps;--but destined by-and-by to become noble reservoirs in which man may pleasantly bathe, and in which little fishes play and shoot to and fro, and hide under the umbrageous fronds of the oar-weed and tangle that droop gracefully into the ample cavity.

CORKWING.

In the pleasant sunny afternoons of this season of the year we may find in tolerable abundance the pretty Cork-wing,[98] in such rock-pools as I have been speaking of. In the shallow hollows of the ledges they shoot hither and thither, the swift movement just catching the collector’s eye; but here they are difficult to capture, owing to the numerous exits and hiding-places among the stones. The deeper basins are pretty sure of containing one or two, and generally of larger size. Here the dip-net can be brought into action, and they are readily taken. But the finest specimens are obtained around the edges of the rocks in the free water, and where there is considerable depth. Here the attentive eye discerns them quietly hovering, some yard or two beneath the surface, deliberately picking their tiny crustacean food from the drooping weeds, or playing to and fro in little parties of half-a-dozen, on motionless or gently undulating fins; a pretty sight to watch. From these seaward edges of the rocks the coarser sea-weeds growing in a thick fringe, when the tide has left them partly exposed, hang their tips in the heaving water; and under this grateful shelter the little Corkwings, as well as other small fishes, their companions, delight to disport themselves, finding copious food in the purple obscurity, and getting many a peep through the latticed leaves at their idler fellows in gamesome play without. If, now, the collector have provided himself with a stiff ring-net, and a long and stout handle, he may sift out, as it were, the tenants of these shades, by collecting, in succession, the drooping weed-tips in the mouth of his net, and lifting it gently through them; when the lovely little emerald fishes will be found, two or three at each dip, struggling and panting and leaping and quivering their helpless fins at the bottom of his bag.

The Corkwing belongs to the great Wrasse family; which, though it chiefly develops itself in the tropical seas, is yet well represented in our own. Yarrell has figured thirteen species, all of them found on our south-western shores, and a few of them ranging to the north as well. The entire family is remarkable for its bright and gorgeous hues, often taking the form of bands, stripes and spots, well defined, and in vivid contrasts. This little species, which extends to the length of five inches, but is much more commonly taken not more than half that size, is of a rich emerald-green hue, lighter beneath, and generally marked with a conspicuous black spot on each side of the base of the tail. Small individuals are frequently found, of a dark reddish brown, arranged in a minute tesselated pattern on a pale ground; and occasionally of a rich golden bronzed hue. The eyes are usually of the finest vermilion.

FIGURES OF WRASSES.