No. 596] EVOLUTIONARY THEORY 



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we have reason to think that it is located chiefly in the 

 nucleus. Similarly we are ignorant of the specific nature 

 of the machinery that determines phylogenetic varia- 

 tions, but we have reason to think that it is located in the 

 germ plasm and that the karyokinetic phenomena, espe- 

 cially the movements of chromosomes at and around the 

 time of fertilization, have a great deal to do with such 

 phylogenetic change. But as the egg with its given in- 

 ternal mechanism of development under adequate ex- 

 ternal conditions will develop into the specific adult form, 

 so the primitive germ plasm with its internal mechanism 

 of evolution under adequate external conditions has devel- 

 oped into all those forms or kinds of germ plasm that 

 are responsible for the great variety of present and past 

 organisms. Just as the egg-nucleus contains probably 

 fewer kinds of molecules, but each more complex, than a 

 nerve cell, e. g., of the adult, so the ancestral form of 

 protoplasm probably contained fewer kind of molecules 

 each more complex than the derived forms. The derived 

 forms, conversely, have more kinds each of simpler 

 constitution. 



In this view (if we may let our imagination picture 

 the consequences) the foundation of the organic world 

 was laid when a tremendously complex, vital molecule 

 capable of splitting up into a vast number of kinds of 

 other vital molecules was evolved! The capacity for 

 thus splitting off molecules determines the possibility of 

 production of the organic species with their vast number 

 of characteristics. 



It is to be kept in mind, however, that the number of 

 genes is probably less than the number of elementary 

 species. For numerous elementary species differ by 

 only one or two genes and in many cases the species 

 differ only in new combinations of the same set of genes. 



This theory of evolution is not new; it is that briefly 

 expressed by Bateson in his Australian address; it is 

 very clearly expressed by Hagedoorn in Roux's "Vor- 

 trage" and has received the support of Lotsy (1913). It 



