320 Heredity, 



ceding generation tlie power to give rise to a new organ- 

 ism with all the established hereditary characteristics of 

 the race; and that each element also had, by virtue of 

 its contained gemmules, the power to transmit varia- 

 Lility. 



The existence, in each element, of the power to trans- 

 mit the hereditary characteristics of the species is obvious- 

 ly superfluous, since the object of sexual union, the trans- 

 mission of a tendency to vary, would be equally well se- 

 cured if only one element had the power to transmit the 

 common characteristics of both parents. I therefore 

 believe that, as organisms gradually increased in size, as 

 the number of cells in their bodies grew greater, and as 

 the differentiation and specialization of these cells became 

 more and more marked, one element, the male cell, be- 

 came adapted for storing up gemmules, and, at the same 

 time, gradually lost its unnecessary and useless power to 

 transmit hereditary characteristics. This process was 

 gradual, and even in the highest animals the power of the 

 male cell to transmit hereditary characters does not seem 

 to be completely lost, although few traces of it remain. 



I also suppose that natural selection has acted upon 

 the various cells of the body to restrain them from 

 throwing off unnecessary gemmules, and that this power 

 is exercised only Avhen a change in the surrounding world 

 renders variation necessary. 



After framing this hypothesis the next step is to test 

 it by applying it to the various observed phenomena of 

 heredity in order to see how far it explains and inter- 

 prets them. I have attempted to do this in chapters VI. 

 to X. of this book, and I think we are justified in conclud- 

 ing, as the result of this review, that, while there are many 

 facts which the hypothesis does not explain, they are not 

 of such a character as to directly contradict it, while it 



