CRA YFISII 



251 



modified in the male for use in reproduction (Fig. 152). The abdominal 

 appendages are known as swimmerets, although they have no function 

 in connection with swimming. The appendages of the last abdominal 

 segment are broad and flat and are called uropods. With the telson, 

 which is a projection of the segment backward in the median line, they 



■Antenna 



Chela 



Uropod 



Telson 



Fig. 151. — Cambarus diogenes Girard, one of the commonest and most widely distrib- 

 uted crayfishes of the United States east of the Rocky Mountains. [From Hagen, Mem. 

 Mi/s. Comp. ZooL, Harvard Univ., vol. 2 {under the name C. ohcsus Hagcn).] X /jj 



form a broad, flat, paddle-like structure used in one form of locomotion. 

 All of these appendages are reducible to a common plan and result from 

 the modification of a typical biramous, or two-branched, appendage. 



In addition to these appendages there are two stalked eyes, attached 

 to the first segment on each side of the base of the rostrum, which can 

 be extended and withdrawn and also pointed in different directions. 



