72 Descriptive Zoology. 



The Senses of the Crayfish. The crayfish appears to 

 have the senses of touch, sight, taste, and smell. 



The Sense of Sight The eyes are on movable stalks. 

 The advantage of being able to project the eyes is ap- 

 parent. The protection afforded by withdrawing the eyes 

 is almost equally apparent when we consider that cray- 

 fishes fight fiercely with each other, besides being frequently 

 under the necessity of protecting themselves from enemies 

 outside of their own race. The projecting rostrum and 

 the sharp blade of the lamina of the antenna need no ex- 

 planation as to their use. The eye of the crayfish is a 

 typical compound eye. It is made up of distinct parts, 

 each of which is called a facet, or cornea. 



The Sense of Touch. One does not need to experiment 

 long with crayfishes to be sure that they feel as well as see. 

 The general surface of the body is more or less sensitive 

 to touch, but with such a hard covering this sense can 

 hardly be other than a very dull sense over most of the area. 

 But the antennae are specially adapted for this sense, and 

 their long, slender, tapering form and jointed structure 

 render them convenient to apply to surrounding objects. 



Smell and Taste. Certain hairs of the external branch 

 of the smaller antennas are believed to be connected with 

 the sense of smell. 



There is in the basal joint of each antennule a sac, 

 formed by the depression of its outer surface, so that free 

 communication is left with the surrounding water. This 

 was long supposed to be an organ of hearing, but is now 

 regarded as the seat of the sense of equilibrium. 



There is no doubt that the crayfish discriminates in 

 choice of food, and we have good reason to believe that 

 the sense of taste is present. 



