GERMINAL SELECTION 151 



many correlated parts, the appearance of useful varia- 

 tions at the proper time, the growth or atrophy of 

 organs (even taking panmixia into account), are as 

 many difficulties which natural selection is powerless 

 to solve without the help of another factor. This 

 factor is, according to Weismann, germinal selection. 

 Thus Weismann avoids Lamarckian explanations, a 

 thing he could not have done if this new theory had 

 not supplemented the theory of natural selection. 



The id ea of germinal selection r est g "pnn wlmt 

 Wilhelm Roux calls "the struggle between the p arts 

 of the organism." Weismann developed Roux's idea; 

 not only is this struggle going on between organs, 

 tissues, and cells, but also between invisible vital units, 

 not only between soma cells, but between germ cells 

 as_ well. 



For example, when the determinants multiply by 

 cleava ge, the daughter-d eterminants thus produced 

 are never alike in size or in faculty of assimilation, 

 for there arise between them, as well~as~n5etween 

 c^HsTtissue s and organs, differences due to the fluctuai- 

 tioii^j)fjthe_foj2d^up^pJy : __Nutrition is, as we know7 

 more than a passive act; a certain element not only 

 assimilates food but deflects it toward itself the more 

 powerfully as it is stronger and endowed with a 

 greater faculty of assimilation. Consequently the 

 s trongest determinants of the germe n will deflect 

 more food and become still stron ger; others, being 



