Amphimixis and Nutritive Irregularities in Germs 195 



not prevented from passing to descendants by the con- 

 jugation of this individual with others which do not 

 possess any such variations, but are only diluted, so to 

 speak. Therefore all that is necessary is to suppose the 

 struggle for existence to be more severe or to have a 

 higher degree of selective capacity than that which would 

 have been sufficient if there had not been sexual repro- 

 duction. 



It is well known further that Weismann, in order 

 to afford natural selection abundant and never failing 

 material upon which to act, has made for himself a 

 weapon of sexual reproduction, attributing to it a great 

 fruitfulness in the constant production of new variations. 

 But he seems to have been partly converted finally to the 

 opposite view of the Lamarckians already mentioned, 

 that sexual reproduction only contributes to securing the 

 unity and constancy of the species. For, in order to ex- 

 plain the production of a lot of fortuitous variations, 

 he finally sought refuge in the unavoidable irregularities 

 of nutrition in the germ plasm, 152 a thing which makes 

 his hypothesis upon the biologic function of amphimixis 

 quite superfluous. It may be merely noted here that when 

 once one sees in amphimixis a cause tending toward the 

 levelling of individual characters and consequently to- 

 ward the fixity of the species, and thereby reducing by 

 so much the probability that the selective capacity of the 

 struggle for existence is alone sufficient, one must then 

 feel so much the more strongly the necessity of discover- 

 ing some cause of variation capable of acting simul- 

 taneously and in the same way upon at least quite a 

 large part of the individuals of the species, and of 



t52 Weismann : Das Keimplasma. P. 541 570. 



