The Evidence from Sexual Characters. 175 



Among the Cladocera, of which the common water- 

 flea of our fresh-water ponds and lakes is an example, 

 the female is provided with a brood pouch, within 

 which the eggs are carried and the young developed. 

 In the male these structures are absent, and the second 

 antennae are especially modified as organs for discover- 

 ing and holding the female. They are richly supplied 

 with sensory hairs, and they are often armed at their 

 tips with grappling hooks, which differ in the males of 

 closely allied species. 



FIG. 7. Antenna of male Cyclops FIG. 8. Antenna of male Cyclop* 

 terrulatus. canthocarpoides. 



The Ostracoda present sexual differences like those 

 in the Cladocera, and in many of them it is certain that 

 the male part deviates, more than the female part, from 

 the typical form. 



In the non-parasitic Copepods, of which the fresh- 

 water Cyclops (Fig. 9) is an example, there is not 

 very much difference between the sexes, although cer- 

 tain appendages, which are unmodified in the female 

 and retain their typical form, sometimes differ greatly 

 in the males of allied species, and may be specially mod- 



