OCEAN LIFE. 39 



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-Mine olfactory.' 



" The 'crust,' or skin which envelopes the body, in these ani- 

 mals, differs from that of INSECTS, inasmuch as it generally 



