24 THE NATURAL HISTORY OF THE COMMON CRAYFISH. 



the eye stalks (1), The antennae are organs of touch ; 

 the antennules, in addition, contain the organs of hear- 

 ing ; while, at the ends of the ejestalks, are the organs 

 of vision. 



Thus we see that the crayfish has a jointed and 

 segmented body, the rings of which it is composed being 

 ver}^ obvious in the abdomen, but more obscurel}^ trace- 

 able elsewhere ; that it has no fewer than twenty pairs 

 of what may be called by the general name of a2^- 

 pendages ; and that these appendages are turned to 

 different uses, or are organs of diiferent functions, in 

 different parts of the body. The crayfish is obviously 

 a very complicated piece of living machinery. But we 

 have not yet come to the end of all the organs that may 

 be discovered even by cursor}^ inspection. Every one 

 who has eaten a boiled cra3'fish, or a lobster, knows 

 that the great shield, or carapace, is very easily separated 

 from the thorax and abdomen, the head and the limbs 

 which belong to that region coming away with the 

 carapace. The reason of this is not far to seek. The 

 lower edges of that part of the carapace which belongs to 

 the thorax approach the bases of the legs pretty closely, 

 but a cleft-like space is left; and this cleft extends 

 forwards to the sides of the region of the mouth, and 

 backwards and upwards, between the hinder margin of 

 the carapace and the sides of the first ring of the abdo- 

 men, which are partly overlapped by, and partly overlap, 

 that margin. If the blade of a pair of scissors is care- 



