COPEPODA. 



393 



f 



indeed the Arthropod char- 

 acter is entirely masked in 

 the females, the bodies pre- 

 senting an ungainly and 

 monstrous appearance with 

 little indication of limbs 01- 

 of segments. The males of 

 these species are however 

 of more normal structure 

 and the affinities are always 

 clearly indicated in the 

 characters of the young. 



The free-swimming forms 

 superficially resemble the 

 macrurous Decapod Crus- 

 tacea in the general contour 

 of their body (Fig. 257). 

 This consists of a more or 

 less oval anterior portion, 

 including the cephalothorax 

 and a number (3-5) of 

 movable thoracic segments, 

 bearing swimming feet ; and 

 of a narrower posterior por- 

 tion, the abdomen, which is 

 without appendages. It 



ends in a caudal fork, consisting of two lateral processes, 

 beset with setae. 



The first abdominal segment carries the generative orifices. The 

 hind part of the body is generally divided off by a constriction which 

 in some forms (Gymnoplea) lies behind the last (5th) thoracic segment, 

 but in others (Cyclopidae, Harpactidae) in front of it. The region be- 

 hind the constriction is called by some authors the urosome. In the latter 

 case the last thoracic segment is included in the nrosome. In the 

 former the urosome is identical with the abdomen. 



The cephalothorax and the anterior free thoracic segments 

 are produced laterally, in Cyclops, into low pleural folds (Har- 

 tog). In female Notodelphyidae (q.v.) a dorsal brood sack 

 is formed in the thoracic region. 



In the free-swimming forms the number of segments of the 

 body, as indicated by paired appendages or by the jointing of 



FIG. 257. Female of Cyclops cumitutus seen from 

 the dorsal surface (after Clans). A', A" the 

 anterior and posterior antennae ; D alimen- 

 tary canal ; OrS egg sacks. 



