Evolution of Sex 357 



union, not of closely similar fundamental germs, but of 

 those circumstantially different; that is to say sexually dif- 

 ferent. 



It is not intended that this description should be taken as 

 the life history of any particular single-celled species. It 

 is an abstract presenting the typical features of a primitive 

 form of sex. The Algae present such an endless variety of 

 methods of reproduction, both sexual and asexual, that 

 almost every possible experiment seems to be proceeding 

 even now; and the student who desires concrete examples, 

 can find them in abundance, in the biological study of that 

 order. 



The process is fundamentally the same whether it be the 

 activity of the single celled Algae or of the germ-cell of a 

 highly evolved multicellular being. In the latter case it has 

 become the only method of reproduction, because it is evi- 

 dently the only method which could accomplish the elaborate 

 transmission of heredity upon which high evolution depends. 

 In the fully developed sex process, normal to the viviparous 

 animals, including mankind, the large or egg cell becomes 

 a "resting" cell as soon as it is mature, and it loses the 

 power to divide in asexual reproduction, which some of 

 the single celled creatures retain. But it remains equally 

 true in all species that the beginning of a new individual, is 

 in the segmentation and development of a single minute 

 germ-cell, which builds up all the rest of the body. 



