CHAPTER XXII.

CRUSTACEA (Crabs and Shrimps).

THE dark, mysterious world of waters hides many a "moving creature that hath life;" and the solitary pacer along the black line of sea-weed that bounds the domains of earth and sea, or the curious Paul Pry that is ever and anon peering into nooks and holes and crannies in the surge-worn rocks, is continually surprised by some strange being, some minim of existence it may be, uncouth and slow, or lithe and elegant, and rapid as lightning; dull and sombre as suits its obscure retreat, or bright and gailytinted from the solar ray; some new combination or modification of organs; some novel exhibition of instinct, habit, or function; that awakens his admiration, and, if he be accustomed to turn from the creature to the Creator, elicits the tribute of praise to Him who made all things for His own glory.

The CRUSTACEA pre-eminently make the waters their home; they are the aquatic division of that mighty host of living things, that range under the title of ARTICULATA. The Insects, Spiders, and Mites, counting their armies, as they do, by hundreds of thousands, leave, with scarcely an exception, the sea untouched; and though a goodly number of these are found in the fresh waters of river, lake,

and pool, they are few compared with the vast body. The solid earth and free air constitute their sphere of existence. The CRUSTACEA, on the other hand, though represented by a few species that crawl on the land, and more efficiently in fresh waters, mostly range the sea, dwelling, according to the diversity of their structure and instinct, from the sunny surface to the unilluminated depths; from the shallows of the shore to the boundless solitudes of the ocean; from the genial waves of the Equator to the icefields of the Pole, to "Arctos and eternal frost."

Nor let this last assertion be considered as a sounding platitude with which to sweep the sentence round gracefully; for it is literally true: as far into the dreary regions of the Pole as our bold explorers, or still hardier whalefishers have penetrated, they report the Arctic Sea to swarm with small CRUSTACEA. One little species, in particular, found in immense numbers beneath the ice, was turned to account in the temporary sojourn of the discovery expeditions in winter quarters. The men had often noticed the shrinking of their salt meat which had been put to soak, and a goose that had been frozen, on being immersed to thaw, was, in the lapse of forty-eight hours, reduced to a perfect skeleton. The officers afterwards availed themselves of the services of these industrious little anatomists, to obtain clean skeletons of such small animals as they procured, merely taking the precaution of tying the specimen in a loose bag of gauze or netting, for the preservation of any of the smaller bones that might be separated by the consumption of the ligaments.

In most respects, CRUSTACEA are so much like Insects, that the older naturalists, and the illustrious Linnæus

among the number, arranged them under the great class INSECTA. They have, however, a greater number of limbs ; the full provision being five pairs of true feet, and three pairs of organs, which (because of a certain ambiguity in their function, like that useful piece of furniture of which we read

"Contrived a double debt to pay,

A bed by night, a chest of drawers by day,")

are called foot-jaws. Besides these, a great number of the species have five or six pairs of jointed limbs attached to the under-side of the abdomen, which are generally used for progression, and are called false-feet. Their mouth is furnished with three pairs of jaws and two pairs of antennæ. It must be borne in mind, however, that the total complement of these members is not found present in every species, some of them being wanting in certain extensive groups.

The researches of a naturalist who has paid much atten

Prawn.

tion to this class, Mr Spence Bate, have shed a flood of

interesting light on the office of the organs last-named.* Any one may easily identify them in the Lobster or Prawn. Take the latter. On each side of the long sword-like and spiny beak that projects above the head, there is an organ consisting of three stout joints, at the tip of which are three threads, of which two are of great length, and formed of numberless rings, and the third is short. These organs, then, constitute the inner pair of antennæ. Below these there is a pair somewhat similar, but they consist each of five joints, and one long thread, with a large flat plate on each side. These are the outer antennæ. The former are the organs of hearing, the latter those of smelling.

In the living animal, the inner antennæ are always carried in an elevated posture, and are continually flirted to and fro with a rapid jerking motion that is very peculiar, striking the water every instant. It is very conspicuous in the Crabs, from the shortness of the organs in question. When next our readers, gazing on the tenants of those wonderful marine tanks at the Zoological Gardens in the Regent's Park, see a Crab tapping the surrounding water, and, as it were, feeling it-they may understand that he is trying it for the vibrations of sound: it is the action of vigilant listening, which never relaxes its guard.

To help the perceptions of the animal, the many-jointed filament which strikes the water is fringed with hairs of great delicacy, standing out at right angles to the stalk, so that the slightest vibrations cannot fail to be conveyed to the sensorium. This may be called the outer ear; but in the interior of the basal joint, which is large and swollen, there is a cochlea, or inner ear, having calcareous walls of

* Ann. and Mag. of N. H., July 1855, p. 40.

delicate texture, to the centre of which passes the auditory

nerve.

The outer antennæ differ greatly from the inner in their internal structure, though they resemble them so much in form. In the Crabs, the basal joints form a sort of box or compact mass, with an orifice on the side next the mouth, closed or opened at pleasure by means of a little door with a hinge, on the interior side of which a long bony lever is fastened, with the necessary muscles attached to it. In the Lobster and Prawn the door is wanting, but the orifice is protected by a thin membrane; ́and in some of the lower forms it is placed at the end of a strong spine or projection. In all cases, however, the orifice "is so situated that it is impossible for any food to be conveyed into the mouth without passing under this organ; and of this the animal has the power to judge its suitability for food by raising the operculum [or door] at will, and exposing to it the hidden organ-the olfactory."* Who can refrain from exclaiming, at the sight of such beautiful, such exquisite contrivances for the safety and wellbeing of creatures so mean, "Great and marvellous are thy works, Lord God Almighty!"

The "crust," or skin which envelopes the body, in these animals, differs from that of INSECTS, inasmuch as it generally contains a considerable portion of carbonate of lime. In many of the smaller forms, as in the Shrimps and Prawns, it takes the consistence of thin transparent horn; but in the larger, as the Lobsters and Crabs, it acquires a great density, is perfectly opaque, and of the hardness of true shell, or even of stone. In the tips of the stout

* Bate, loc. cit. p. 44.