CRUSTACEA 



299 



fused in others; it is less obvious in other cases in which it occurs. 

 Thus the full possible number of joints in the protopodite is four. 

 Some authorities, however, prefer to regard the preischium as part 

 of the endopodite, in which case the protopodite has only three joints 



Fig. 211. Limbs of Crustacea. Not drawn to scale. After various authors. 

 A, Maxilla of Mysis larva of Penaeus (Decapoda). B, Maxilla of Acanthosoma 

 larva of Sergestes arcticiis (Decapoda). C, Second trunk limb of female 

 Cyclestheria hislopi (Conchostraca). D, Mandible of Calaniis. E, Thoracic 

 limb of Nehalia. F, Mid-thoracic limb of an euphausid. G, Swimmeret of 

 the crayfish, bp. basipodite; br. branchia (epipodite); cp. coxopodite; en. en- 

 dopodite; ep. epipodite; ex. exopodite;^6. fiabellum (exopodite); gn. gnatho- 

 base; pr.cp. precoxa; 1-9, endites or segments of the limb. 



at the most. Epipodites, when they are present, are borne upon the 

 precoxa {proepipodites) or coxopodite {metepipodites). 



The endopodite is usually segmented. If the preischium be not 



