32 Elementary Zoology. 



It has been said that the cephalo-thorax represents a 

 number of fused segments of the body. This is proved by 

 three principal facts; in the first place, the general structure is 

 the same, divisible into terga, sterna, epimera, etc. ; secondly. 



CXf. 



Fig. is.— Abdominal appendages of Crayfish. (After Huxley.) 



A, first appendage of male ; B, do. of female ; c, second pair of male ; d, e, .succeedin|r 

 swimmerets ; F, tail swimmerets ; en.fi^ endopodite ; ex.p, exopodite ; *./, basipodite; 

 cx.pt coxopodite ; a, b^ divisions of endopodite. 



the Sterna are separate, and finally, to each sternum corresponds 

 a pair of appendages. 



The posterior end of the body is formed by a two-jointed 

 plate, the tehon., which is not usually regarded as having the 



