THE CRUSTACEA 



distinguished. The two rami may become specialised for different 

 functions, as in the case of the thoracic limbs of Malacostraca 

 (Fig. 3, D, E), where the endopodite forms a Avalking-leg, while the 

 exopodite becomes a swimming-branch or may disappear altogether. 



9"^: 



Fig. 3. 



Various types of Crustacean limbs. A, abdominal limb (pleopod) of Crayfish. (After Hux- 

 ley.) B, swimming-foot of Calanus (Copepoda). (After Sars.) C, limb of second pair 

 (antenna) of nauplius larva of Apns (Branchiopoda). (After Claus.) D, first thoracic limb 

 of A nasjndes (Syncarida). E, second thoracic limb of Anaspides. bs, basipodite ; ex, coxo- 

 podite ; en, endopodite ; ep, epipodite ; fx, exopodite ; gn, gnathobase ; prof, protopodite. 



The coxopodite often bears on the outer side an appendage (rarely 

 more than one), known as the epipodite, which may function as a gill. 

 In the appendages near the mouth one or both of the segments of 

 the ])rotopodite may develop, even in the nauplius, inwardly-timied 

 masticatory processes or (jnathohases. The occurrence of epipodites 

 and gnathobases suggests that the primitive Crustacean limb was 



