158 ELEMENTARY BIOLOGY. [CHAP. xn. 



d. The auditory sac in the crayfish is very similar to 

 that in the lobster, and may be examined in a 

 similar way. It is however not so good, both 

 on account of its smaller size and because the 

 auditory hairs, although longer, are collected in 

 a close tuft, which makes it more difficult to see 

 the manner of their insertion. 



