COPEPOUA. 



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 seta? (fig. 339). 

 In the femalf, 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. 



FIG. 339. Female of Cyclops corona tin, seen FIG. 310. An antenna of the male of 

 from the dorsal surface. D, intestine ; OcS, Cyclops serrnlatiis. Sp, olfactory hairs . 

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



The anterior antenna?, 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 

 dining copulation (fig. 340). The posterior antenna* are always 

 shorter, and not unfrequeiitly bifurcated and adapted for clinging 

 to surrounding objects. With regard to the oral appendages 



