38 



Elementary Zoology. 



to manducatory limbs, brought about by the growing im- 

 portance of the protopodite and lessening importance of the 

 endopodite and exopodite. It may be mentioned that the con- 

 joined exopodite and epipodite of the second maxilla is often 

 called the scaphognathite ; it serves to create a current of water 

 through the branchial chamber, and thus to renovate the 

 body through the oxygen absorbed by the branchiae. 



Fig. 19.— Mouth appendages of Crayfish. (After Huxley.) 



A, mandible ; b, first, c, second, maxilla ; /, palp ; b.p, basipodite ; cxp, coxopodite ; 

 en, endopodite ; sgy scaphognathite. 



Besides the appendages that have been already enumerated, 

 the crayfish possesses two other pairs. These are the antenna 

 and the anten?iuks. The antennae, which form the second 

 pair of these, are shown in Fig. 20, C. Each consists of a basal 

 piece, two-jointed, which may be compared with the proto- 

 podite of other limbs. With this articulate, firstly a scale-like 

 structure, the scaphocerite, which is perfectly movably articulated, 



