24 THE NATURAL HISTORY OF THE COMMON CRAYFISH. 
the eye stalks (1). The antenne are organs of touch; 
the antennules, in addition, contain the organs of hear- 
ing; while, at the ends of the eyestalks, 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 
very obvious in the abdomen, but more obscurely trace- 
able elsewhere ; that it has no fewer than twenty pairs 
of what may be called by the general name of ap- 
pendages; and that these appendages are turned to 
different uses, or are organs of different 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 cursory inspection. Every one 
who has eaten a boiled crayfish, 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- 
