MATING 61 



For the purpose of reproduction in all the higher 

 animals, it becomes necessary that the two kinds of 

 sex cells (male and female) shall be brought together 

 in the process of fertilization in order to produce the 

 new being. In many animal species the separation 

 of the two sexes is, however, not complete, each 

 individual possessing both male and female sex cells. 

 Such individuals are called hermaphrodites (from 

 Hermes and Aphrodite, the Greek god and goddess). 

 But usually a hermaphrodite does not fertilize itself, 



FIG. 30. VOLVOX MINOR, WITH SEX CELLS. (After Stein.) 

 sz, Body cells ; fez, germ cells. 



(From Weismann, " The Germ-Plasm.") 



but acts either as a male or as a female individual, 

 mating in a proper sexual manner like the sexual 

 organisms. 



There exists one exception to the general rule of 

 sexual reproduction in the higher animals. There are 

 some animals whose females have the power of re- 

 production without needing the help of the males. 

 The males appear only at certain seasons, and then 

 sexual reproduction is possible. In some species, 

 males have never been found. Such reproduction is 

 called parthenogenesis or virgin-reproduction (par- 



