THE PHYSIOLOGY OF THE COMMON CRAYFISH. 



There is much reason to believe that odorous bodies 

 affect crayfish ; but it is very difficult to obtain experi- 



FlG. 26. Astaciis flwviatilis. A, the right antennule seen from the 

 inner side ( x 5) ; B, a portion of the exopodite enlarged ; C, olfactory 

 appendage of the exopodite ; a, front view ; b, side view ( x 300) ; 

 a, olfactory appendages ; au, auditory sac. supposed to be seen through 

 the wall of the basal joint of the antennule ; b, setae ; en, endopo- 

 dite ; ex, exopodite ; sp. spine of the basal joint. 



mental evidence of the fact. However, there is a good 

 deal of analogical ground for the supposition that some 

 peculiar structures, which are evidently of a sensory 



