Part 10

A close ally of this form is a pretty shell which we often obtain by dredging, called the Cup-and-Saucer Limpet. It is a pretty little white porcellaneous cone, with a curved plate of thin shell projecting from the side of the interior, like a semi-cup within the cup. It is named _Calyptræa_. Both this and the Torbay Bonnet have been ascertained to manifest domestic instincts, in sitting on their eggs till they are hatched. According to MM. Audouin and Milne Edwards, the parent _Calyptræa_ “disposes them under her belly, and preserves them, as it were imprisoned, between the foot and the foreign body to which she adheres, her patelloid shell thus serving not only to cover and protect herself, but as a shield to her offspring. These eggs are oval bodies of a yellow colour, enclosed in membranous capsules, which are elliptical, flattened, translucid, and filled with an albuminous matter. The number of these little capsules varies from six to ten; they are connected among themselves by a footstalk, so as to represent a sort of rosette; each of them contains from eight to ten eggs. It appears that the young _Calyptræa_ are developed under this sort of maternal roof, and do not quit it until they are in a condition to affix themselves, and are provided with a shell sufficiently hard to protect their own bodies.”[74]

LOCUST SCREW.

Along the margins of these shallow rock-pools with sandy bottoms, we see many little grey shrimp-like creatures, with thick-set arching bodies, which swim rapidly, and with much vibration of the abdominal feet, from weed to weed. If we catch one and lay it on the rock or on the wet sand, it appears very helpless, for its vertically thin shape and arched attitude preclude the possibility of its crawling: it falls upon its side, and vainly struggles round and round as on a pivot, or makes aimless jerks by throwing out the tail. It is of a greenish blue, or glaucous colour, marked with red dots. This is the common Locust Screw,[75] which is so confined to sea-water, that it has been affirmed that if put into fresh water it presently dies. But the experiments of Mr. Robertson negative this statement:[76] he has found that five out of seven, after being eighteen hours in rain-water, continued to live upon being returned to salt water.

I delight to trace the manifestations of parental love in these tiny forms of animal life. It had long been known that the females of this species display a solicitude for their infant offspring, which they carry for some time about with them; but the following very pleasing details of maternal manners have recently been observed by my relative, Dr. James Salter, and by him communicated to the learned zoologists who are now engaged upon the history of this order:--

“On catching a female with live larvæ, nothing is seen of the progeny till the parent has become at home in the aquarium, when the little creatures leave her, and swim about in her immediate neighbourhood. The plan I have adopted to watch this curious habit of maternal protection has been to place a single individual in a bottle of sea-water. After a time, and that soon, the little crustacean seems at ease, and swims slowly about, when the young fry leave, and swarm around her in a perfect cloud; they never leave for more than half or three-quarters of an inch, and as she slowly moves about they accompany her. If, now, one taps the sides of the bottle with one’s finger-nail, the swarm of larvæ rush under their parent, and in a second are out of sight. The parent now becomes excited, and swims about quickly, as if trying to escape; but on letting the bottle containing her rest quite still on a table, she soon gets composed, when out come the young larvæ again, and swim about as before. This may be repeated as often as the observer wishes, and always with the same result. I have only seen this in one species, but it is quite a common species in Poole Harbour, and I have watched the interesting habit many times.”[77]

FRESH-WATER SCREW.

Every little stream and ditch of running water in our lanes and fields abounds with a species, which, except for the fresh-water habit, and a little difference in the shade of colour,--the latter being of a yellowish, instead of a bluish grey,--is so absolutely identical with the Locust Screw, that, notwithstanding it is registered under a name of its own, _Gammarus pulex_, it is difficult to believe that the two are not of common parentage. Certain facts observed in Sweden give colour to such a suspicion. The large inland seas of fresh water, Lakes Wetter and Wener, in the south of that country, are situated on high ground, and have the surface of their water 300 feet above the level of the Baltic, whereas the bottom is 120 feet below such level. In these lakes (which appear to have been lifted up with the gradual uprising of the country) have been found several genera and species of Crustacea, three of which are AMPHIPODA, which are affirmed to be identical with marine ones, viz., _Gammaracanthus loricatus_ (Sabine, Ross, Kröyer), _Pontoporeia affinis_ (Lindström), and _Gammarus cancelloides_ (Gerstfeldt).

The first is now only known to exist in the Arctic seas, the second in the Baltic, and the last was found in Lake Baikal, in Central Asia. It is therefore suggested by Lovèn, that the land was raised so as to convert these waters from marine bays into inland lakes. These marine species were retained within the basins, the waters of which have since been changed, through the agency of springs, into fresh water; and with the gradual transfer of the water, the habits of the animals have also changed gradually, and that without any outward alteration of form. Professor Lovèn thinks that there is sufficient evidence to show that this change in the condition of these lakes must have taken place during the great glacier period, at a time when the animals now found in it (and which are known at this day only to inhabit the extreme north) could have lived in the same latitude as the south of Sweden. The evidence of these fresh-water lakes suggests that similar changes in the relative position of sea and land may have been the cause of our having fresh-water Crustacea nearly allied to marine species in our rivers and inland streams.[78]

Crawling about perpendicular faces of rocks, generally at a considerable distance above high-water mark, we may find a crustacean, not very remotely allied to these, of rather large size.[79] It is broad and flat, a form which marks it as belonging to another order, though in many peculiarities of structure agreeing with its near neighbours the high-backed Screws. The present species crawls readily with its fourteen short strongly-hooked feet, with which it clings to every little roughness of the stone. It swims much less effectively: indeed, I have never seen it spontaneously in the water; and those which I have captured on the rocks, and transferred to an aquarium, have died after a very brief interval. They have little agility under any circumstances, and trust rather to craft than to power for their safety. When alarmed, they instantly gather in their feet, and drop from their hold; and, as I have said that the positions in which they are found are for the most part perpendicular surfaces, such as cliffs and sea-walls, their one trick is often successful.

SEA WOODLOUSE.

Thus the _Ligia_ makes a decided approach to an aërial or terrestrial mode of life; which, indeed, is strictly the habit of some species with which every cultivator of flowers is only too familiar. I refer to the little Woodlice, or Buttons, or Sows, as they are variously called, so abundant in gardens, especially in pits and frames, and so annoying for their depredations on our cherished plants. These garden pests are scarcely to be distinguished as to their structure from the semi-marine _Ligia_, particularly those flatter and softer species (_Porcellio_), which do not roll their body into a complete ball.

In all these creatures we find maternal care. The females carry their eggs in a sort of pouch or sac, placed beneath the breast, which opens when these are hatched to afford exit for the infant progeny. These have from the first the same form and appearance as the adult, except that they have at first six pairs of feet instead of seven. They cling about the body of the mother, and are carried by her in her rovings with affecting solicitude.

About the sloping ledges of low-lying rock, especially those which are covered with young mussels, so closely that between their blue-black shells, packed and tied together with byssus-threads, you can scarcely thrust a penknife, we very commonly see slender Worms of a vivid grass-green hue gliding in and out. Their movements are very graceful, and if we examine them closely, we discern the presence of a multitude of minute points along each side of the body, which in turn are thrust out and as quickly retracted. If we put the little creature into a vase of water, we see fresh powers and organs of locomotion; for the back bears a double series of leaf-shaped fins, overlying one another, which act as broadoars rowing the lithe and graceful worm through the sea.

RAINBOW LEAF-WORM.

This species[80] is not more than three inches in length; but there is another[81] much less common, which is larger, richer in colours, and altogether a finer species. A specimen which I lately found was about a foot in length when crawling, and nearly a quarter of an inch in width. The whole body was divided into distinct segments, which in this individual were about two hundred and ten in number; though, according to MM. Audouin and Milne Edwards,[82] they sometimes amount to nearly five hundred, and the worm has been found two feet in length. The head is small, terminated by two pairs of very minute antennæ, but surrounded at what we may call the neck by four pairs of rather long feelers (tentacular cirri), with a fifth pair which are minute and rudimentary.

The colours are very beautiful. The leaf-like fins of the sides, which are somewhat heart-shaped, are of a yellowish green hue, occasionally clouded with blackish; the middle portion of the back, which is exposed, is of a rich brown, but flushed with the most glowing iridescence of blue and purple; while the whole under parts are of a pearly flesh-colour. As it crawls over the stones, it throws its body into the most elegant lateral curves, while its suppleness and great length cause it to cling close to the rock; and thus its outline takes the form of every projection and depression over which it is wandering.

When disturbed, and often without any apparent provocation, we see the under side of the tiny head rise from the ground, swell out, and turn itself inside out, as you turn a stocking, until a great pear-shaped bag is protruded, fully eight times as long, and thrice as broad as the entire head. Its whole surface is rough and papillose, and around its extremity, which is the largest part, there is a row of small knobs or warts. This curious organ is found under similar conditions in very many Annelids; it is commonly called the proboscis, or evertile œsophagus; but in truth it is a special and peculiar apparatus, with little analogy with anything found in higher animals: it is in some species furnished with strong horny teeth, and is doubtless employed for the capture of living prey, and the conveyance of it to the stomach.

The tail of the specimen I refer to was evidently being renewed after having been accidentally lost. For the body-segments ended abruptly, and were followed by a portion, not more than an eighth of an inch long, white, and excessively delicate; but which, when examined with a powerful magnifier, displayed a division into segments, each segment carrying its proper cirri; I could count twenty segments within that minute space, the last of which carried the usual pair of stylets.

REPRODUCTION OF ORGANS.

I find among my notes a record of a specimen of _Phyllodoce_, which, if not identical with this, was closely allied to it, in which I observed the continuance of vitality after the severance of the creature into parts. It was sent to me from Torquay, when I lived near London. When it arrived I found that about an inch and a quarter of the anterior extremity was detached from the remainder, which measured about four inches. The former was motionless, contracted, and seemed lifeless; the latter moved freely. I put both into an old aquarium. The long posterior portion glided about among the stones for two days, exactly like a living healthy animal; the anterior part remained motionless and contracted until the third day, when I saw it also gliding over the stones in a most lively manner, rearing its head, and feeling about in the manner of a caterpillar. Eight days after its arrival, the head portion was still active and apparently healthy, but the hinder part had become motionless and was evidently dead. I find no further record of the case, and probably the anterior part ultimately died without reproduction; but the length of the period of its survival in apparent vigour, renders it not improbable that in the open sea, under the influence of abundant oxygen, and suitable food, the wanting parts might have been renewed to the fore-part, if not to both.

To return to my more recent captive, however. I killed it for cabinet preservation by putting it into fresh water, where it presently died, with the noticeable circumstance that it threw out mucus in such profusion that the whole body was enveloped in a mass, much thicker than itself, of clear jelly, excessively tough and tenacious.

The most common members of the class _Annelida_, that we meet with in these situations, are different species of the genus _Nereis_, which are for the most part worms of considerable size, usually brown or green, with a changeable metallic lustre above, and brilliantly pearly beneath. They have a distinct head, of a squarish form, terminating in two swollen fleshy knob-like antennæ, and furnished with four pairs of thread-like tentacular cirri, which project on each side like a cat’s whiskers. The body is plump, though somewhat flattened, and bears on each side a row of fleshy foot-warts, which are pierced for the extrusion of the curious bristles that are so characteristic of these marine worms.

PEARLY NEREIS.

We can scarcely turn one of these flat stones which lie half-buried in sandy mud at the water’s edge without finding one or more of this tribe. Let us try. Here at once is a specimen, one of the finest as well as one of the commonest of all.[83] The upper surface is of a warm fawn-brown; but the beautiful flashes of iridescent blue that play on it in the changing light, and the exquisite pearly opalescence of the delicate pink beneath, are so conspicuous as to have secured it the title of “Pearly,” _par éminence_. As you gaze upon it you see the great dorsal blood-vessel or heart, as a dark red line running along the middle of the back. This, at irregular intervals of five to fifteen seconds, contracts almost to invisibility, and then expands again, taking the form of a string of beads in each process.

This, however, is only a part of the great circulating system in this fine worm. In it the red blood flows from the tail towards the head; at the under side of the body, there is a similar vessel (the ventral), through which the blood flows from the head towards the tail. Besides these, there are four other longitudinal vessels in the interior of the body, one above and one below the intestine, and one on each side, all of which are connected by transverse branches. Thus there is a double circulation. “The great dorsal,” says Dr. Williams, “the reservoir of the centripetal streams of the body, may be likened to a right ventricle (the lungs cut off), and the great ventral to a left ventricle. The duty of the former is to collect the refluent blood of the system; of the latter to circulate it again.”

Our _Nereis_ is furnished with two pairs of dark blue eyes, and with an evertile proboscis, which consists of two segments. The one first protruded is beset on its upper side with some largish horny points, arranged in two groups, which are continued round to the under side in a band of irregular lines of points. The second segment has four groups of points, the groups of oblong outline, radiating from the strong black jaws, which are protruded last, and can be widely opened and closed.

Here, too, we have an Annelid of very different form and appearance.[84] It is a mean-looking worm, about an inch and a half long, of flattened shape, blunt at each end, apparently covered with a smooth skin of a dull brown colour; but on being touched it presently throws itself into elegant serpentine curves, and then what appears to be the upper skin is seen to be composed of a great number of round flat membranous plates or shields, arranged in two rows overlapping each other. These, though of large size, are attached to the body only by a small point in the centre of their under side, so that when the animal moves, the edges of these shields are lifted, and reveal their true structure, sliding upon one another in a singular manner.

In captivity I have found the animal inert, prone to seek concealment in the corners of the glass vessel beneath other animals or stones, and remaining still for a long time together; but, if disturbed, manifesting impatience and much agility, swimming through the water with strong lateral undulation, as already described. I have been struck with the deciduous character of the broad leaf-like shields. As soon as the animal was in my possession, one and another of these appendages was cast off at almost every time that I roused it to action; and even when allowed to remain quiet, the denuding process went on, so that in a few days it was nearly half naked. This process of self-mutilation will sometimes go on till scarcely a single shield remains out of the double series.

SCALE-WORM.

This dull-coloured Scale-worm presents peculiarities of structure which are eminently worthy of careful examination. The body, like that of the other species we have just been considering, is composed of many rings or segments, each of which bears on its upper surface a little wart or tubercle on each side, to the summit of which is slightly attached the circular leaf-like shield just described. Beneath the shadow of this broad shield the segment projects laterally into another tubercle, whence issue the organs of motion, which in these Annelids are of highly curious structure. In this species they consist of a bundle of straight bristles of exquisite tenuity, and having a silky lustre; they are of unequal length, the upper ones being the longest, and the pencil diminishing pretty regularly downwards. The microscope shows them to be about one hundred in number in each bundle; and each bristle to be a delicate oar consisting of a slender stem, apparently tubular, dilated at the tip into a narrow blade terminating in a minute hook. A fibrous structure is seen to run diagonally across the blade, the edge of which is set with minute barbs pointing outwards, resembling very fine and very short bristles. The whole bundle is connected with a long slender rod of cartilage, which, doubtless acted upon by proper muscles, moves to and fro through the muscular sheath, protruding the bundle of bristles, or entirely retracting them within the body. The bristles, when protruded, slightly diverge, so that the dilated blades of these hundred oars strike with full force upon the water in rowing, if such indeed is the nature of their action, as some have supposed. In the act of withdrawal, however, into the narrow compass of the muscular sheath, the blades slide one upon another, so as to present a surface considerably diminished. But why is each bristle hooked and barbed? The obvious supposition is that these organs act like the pole of a ferry-boat in the shallows; the barbs, pointing outwards, serving to catch any roughness of the surface, and thus to _push_ the animal by their resistance, while the terminal hook may serve to _pull_ in an analogous manner. But then the barbed and hooked edge is the _upper_ one of each oar, a circumstance which renders such an explanation at first sight unsatisfactory. Perhaps, however, the habit of the animal of living under stones, may in some measure account for it; the edge and point of each bristle being intended to act upon the surface of the object above it, beneath which it is forcing its way.

A secondary pencil of bristles also issues from the upper side of each of these tubercular sheaths, so as to project diagonally upwards and outwards beneath the edge of the shield-leaf. This pencil consists of between thirty and forty bristles, which are connected with a cartilaginous rod exactly similar to that of the primary bundle. These bristles run off to a very fine point, and each one is marked on both sides with serratures so delicate as to be only just discernible with a magnifying power of 300 diameters. There are thus about 270 movable bristles of exquisite structure in each segment, which multiplied by 36, the number of segments in the body, gives a total of 9720 distinct organs of motion possessed by this animal, besides the broad leaf-like shields, which perhaps may act as fins, and the short tentacular feet, one of which is placed beneath the primary bristle-sheath, on each side of the segment.

By dissection after death, I have found the proboscis in the form of a long oval sac, very muscular and firm, of a blackish hue, lying in the anterior part of the body, which, on being cut open, showed four horny teeth placed in its neck so as to meet each other in the centre. I have never seen the protrusion of this organ during life, but if it is capable of being wholly everted, as in many species, these teeth must be turned on the outside, where they would seem to be of little use. Possibly, however, the version may be only just sufficient to bring these teeth to the margin, when their action might be made very efficient by the slightest alteration in the contraction of the sac.

Some species of this genus construct for themselves enveloping tubular cases, out of mucus given off from their bodies, and fragments of shells. In these they ordinarily live concealed, but are sufficiently active when they leave their houses. Some shine with a phosphorescent radiance in the dark.

In the great class of Worms, special organs for locomotion are often altogether lacking; and, where found, are only rudimentary. Alternate swellings and contractions of certain portions of the body are a great source of progression; and these are effected by the fluids of the interior, which are driven to a given part of the cavity, and momentarily imprisoned there by the contraction of the circular tegumentary muscles before and behind it; the body swelling at that place. “The muscles of the integument are then excited to action, and the fluid is forcibly compressed forwards or backwards, according to the direction of the muscular agency. Nearly all Annelids are struck with paralysis when this fluid is made to escape from its cavity by a puncture through its external walls. The power of voluntary motion is suspended; the body of the worm becomes passive and flaccid.”[85]

GOODNESS OF GOD.