THE CLASSIFICATION OF CRUSTACEA 49 



more than the first three or four of the thoracic 

 somites. The eyes are not stalked, and are usually 

 fused together to form a single organ on the front 

 part of the head. Swimming branches (exopodites) 

 are usually present on some of the thoracic legs, at 

 least in the males, which are more active swimmers 

 than the females. In the males, also, the swimmerets 

 of the abdomen are often more or less developed, 



FIG. 18 Diastylis goodsiri, ONE OF THE CUMACEA. ENLARGED. 

 (From Lankester's " Treatise on Zoology," after Sars.) 



a', Antennule ; l l -l 5 , the five pairs of walking legs ; m, brood-pouch ; 

 ps, " pseudo-rostrum " formed by lateral plates of the carapace ; 

 t, telson ; ur, uropods 



but they are always absent in the females. The 

 uropods do not form a tail-fan, but are slender 

 forked rods carrying comb-like rows of spines, said 

 to be used in cleaning the anterior appendages from 

 the mud among which these animals generally live. 

 The telson is often absent, or, rather, it is coalesced 

 with the last somite of the abdomen. Under the 

 side-fold of the carapace on each side lies, as in the 

 4 



