1 52 CRUSTACEANS. 



they can be laid flat, and thus protected from injury. The organ 

 of hearing is a cavity closed by a delicate membrane, situated at 

 the base of the second pair of antennae in the lobster and similar 

 forms. In the crabs this is replaced by a small, moveable, shelly 

 disk, pierced with a hole, over which an elastic membrane is 

 stretched. A cavity filled with fluid in each case conveys the 

 vibrations of sound to the proper nerves. 



There can be little doubt that the higher Crustaceans are 

 guided to their food by a sense analogous to that of smell ; but 

 where its seat is placed, zoologists have not determined : the 

 probability is, that it may be connected with the first pair of 

 antennae. Similar observations may be applied to the percep- 

 tions of taste : the sense doubtless exists, and its organ is sup- 

 posed to be the delicate membrane that lines the mouth and the 

 throat. It is commonly considered that the sensations of touch 

 can be but very feebly, if at all, conveyed through the hard cal- 

 careous crust with which these animals are clothed, and that this 

 sense can hardly exist, except in those parts which remain soft 

 and undefended by the crust. But we have seen a swimming crab 

 (Matutd) hold its prey in one claw, while with the other it picked 

 off morsel by morsel of the flesh, and conveyed it to its mouth 

 in a manner which sufficiently evidenced the sensation of touch 

 in these organs ; and we have watched a beautiful West Indian 

 crab (Goniopsis ruricold) feeding itself in the same manner, pick- 

 ing up, now with one claw, now with another, minute atoms of food 

 from the surface of the mud over which .it marched, with a rapidity 

 and a precision which seemed to indicate that a very delicate 

 sense of touch resided in those shelly claws. MR. GOSSE. 



The periodical casting of the shell, or moulting, is a very re- 

 markable feature in the economy of these creatures. Frequently 

 during their lives their hard and shelly covering is cast off in 

 one unbroken piece, so as to present an exact counterpart of the 

 perfect animal. Every part of the integument is thus renewed : 

 nothing is wanting in the cast-off skin the antennae, the jaws, 

 the eyes, are all there, every hair is represented by the case which 

 enclosed it. Even the shelly plates from which the muscles 

 originate, the tendons by which they are attached to the shell, 

 the internal skin of the stomach, and the teeth which are hidden 

 there, are found connected with the rejected shell ! 



The pressure of the old shell being removed, the animal sud- 

 denly increases in bulk, the new skin, as yet soft and flexible, 

 allowing at first of great expansion ; but it rapidly hardens, a 



