CRUSTACEA OCEAN LIFE "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. In most respects, CRUSTACEA are so much like insects, that the older naturalists, and the illustrious Linnaeus 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 • are called foot-jaws. Besides these, a great number of the species have five or six pairs of jointed limbs attached to the underside 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 antennm. It must be borne in mind, however, that the total complement of these members is not found present in every spe cies, some of them being wanting in certain extensive groups.— The researches of a naturalist who has paid much attention 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 antennae.— 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 antennae. The former are the organs of hearing, the latter those of smelling. In the living animal, the inner antennae 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. 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 senso rium. 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 delicate texture, to the centre of which passes the auditory nerve. The outer antennae 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.' " The 'crust,' or skin which envelopes the body, in these ani mals, 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 in 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 claws of the Crab, we see it at its maximum of induration.