232 DEVELOPMENT AND HEREDITY. 



very important part in organic evolution. It seems 

 as though it might have originated among single- 

 celled animals, by the effort of simple protoplasmic 

 masses to absorb each other as food. Such a mutual 

 effort between two individuals would, in all proba- 

 bility, end in a drawn battle by the commingling of 

 the two masses of protoplasm. The sudden super- 

 lative growth — the doubling in size — would of itself 

 induce reproduction, i.e. subdivision, — the new gen- 

 eration would be formed of protoplasm derived from 

 the mixture of both parents, and would inherit devel- 

 opmental potentialities from each. 



But, beside this double inheritance, there is 

 another very important feature of sexual reproduc- 

 tion ; for although each of two organisms may be 

 capable singly of reproducing, yet the process of 

 conjugation gives a peculiar stimulus to the devel- 

 oping germ, which entails a more complex or a more 

 complete development. That this mixture of pro- 

 toplasm derived from two organisms is largely of 

 the nature of mere stimulus to growth activity, is 

 shown by the fact that among many organisms 

 accustomed to reproduce asexually, there may be 

 produced, without fusion of protoplasm, a germ 

 which will attain only a partial development soon 

 arrested, or perhaps develop into a weak individual. 

 A germ thus produced, and a germ produced by 



