COPEPODA. 



429 



the corresponding thoracic segment may be entirely absent. The 

 abdomen as well as the thorax consists of five segments, but is with- 

 out appendages and ends in a caudal fork, the branches of which are 

 furnished at their points with several long caudal setae (fig. 339). 

 In the female, the two first abdominal segments usually unite to 

 form a double genital segment, on which the genital openings are 

 placed. The abdomen, especially in the parasitic forms, very fre- 

 quently undergoes a considerable reduction. 



Fro. 339. Female of Cyclops coronahis, seen FIG. 310. An antenna of the male of 

 from the dorsal surface. D, intestine ; OvS, Cyclops serrulatus. Sf olfactory hairs . 

 ovisacs ; A', A' 1 , antennae. M, muscles. 



The anterior antennae, which are usually many- jointed, bear olfac- 

 tory hairs, but serve in the free-swimming forms for locomotion, and 

 in the male as prehensile arms for catching and holding the female 

 during copulation (fig. 340). The posterior antennae are always 

 shorter, and not unfrequently bifurcated and adapted for clinging 

 to surrounding objects. With regard to the oral appendages 



