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 walking-leg, while the 

 exopodite becomes a swimming-branch or may disappear altogether. 



---p. 



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 Apus (Branchiopoda). (After Claus.) D, first thoracic limb 

 of Anaspides (Syncarida). E, second thoracic limb of Anaspides. 6s, basipodite ; ex, coxo- 

 podite ; en, endopodite ; ep, epipodite ; ex, exopodite ; gn, gnathobase ; prot, 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 protopodite may develop, even in the nauplius, inwardly-turned 

 masticatory processes or gnathobases. The occurrence of epipodites 

 and gnathobases suggests that the primitive Crustacean limb was 



