THE BREEDING HABITS OF ANIMALS 20o 



different methods of copulation, care of eggs, and care of offspring. The 

 habits of disseminating the sexual elements freely into the surrounding 

 medium, of laying unfertilized eggs, and of neglecting the offspring are 

 found most commonly among the aquatic species or species with an aquatic 

 larval period; while the habits of introducing the sperms into the body of 

 the female, the lajdng of fertilized eggs, ovoviviparity and viviparity, and 

 parental care or the birth of young in advanced stages prevail in terres- 

 trial forms. 



The almost endless variety of breeding habits described in the fore- 

 going pages does not, however, entail a corresponding diversity in develop- 

 ment. The fundamental features of the formation of germ cells and of 

 the development of the fertilized egg, described in the following chapter, 

 are very similar in all members of any large group of animals. 



