206 



LIFE, IN ITS INTERMEDIATE FORMS. 



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 con- 

 veyed into the mouth without passing under this organ ; 

 and of this the animal has the power to judge its suit- 

 ability for food by raising the operculum [or door] at will, 

 and exposing to it the hidden organ — the olfactory"* TTho 

 can refrain from exclaiming, at the sight of such beautiful, 

 such exquisite contrivances for the safety and welibeing 

 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 gene- 

 rally 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 hom; 

 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 



* Bite, loc. cit. p. 44 



