CRUSTACEA 281 



name the common fresh-water representative bears, have but 

 a single central eye. 



Secondary sexual differences exist in most of the species, 

 and in some are developed to an extreme degree. The males 

 are generally smaller and more active, and their anterior 

 antennas, as well as the legs of the last pair, more rarely the 

 posterior antennae and the second pair of maxillae, are 

 specially modified to serve as accessory organs of copulation, 

 that is organs for seizing and holding the female, or for 

 attaching the spermatophores to the body of the latter. The 

 females carry the eggs usually in clumps or strings attached 

 to the tail. In these clumps or strings the ova are held 

 together by a hardened secretion produced by the female. 

 In one family (Notodelphyidae) the ova are carried in a dorsal 

 incubatory pouch. In copulation the male attaches one or 

 several spermatophores to the genital segment of the female. 

 The spermatophores are packets of spermatozoa formed by a 

 gelatinous secretion of the vas deferens. In the common 

 fresh-water Cyclops the anterior antennae of the male are 

 thickened and provided with a special hinge-joint, by means 

 of which the male seizes the female by her fourth pair of 

 swimming legs, and then bending up his tail deposits two 

 speramtophores on her genital segment. 



In all the Cyclopidae both of the anterior antennae are 

 thus modified for purposes of copulation, and the same arrange- 

 ment occurs in the Harpactidae. 



In the Calanidae the chief peculiarities of the males, 

 according to Giesbrecht, perhaps the greatest authority on 

 Copepoda, are the following: On the antennae the aesthetic 

 or perceptive vesicles, which are probably olfactory organs, 

 are more numerous and larger; the fifth pair of feet are 

 modified to form a grasping organ; and thirdly, there are 

 five distinct somites in the abdomen (or tail), the genital 

 aperture being on the left side of the first somite. 



