138 EVOLUTION 



the other hand, there are also many heritable 

 characters which blend, and do not conform 

 to the Mendelian mode of inheritance. In 

 illustration we may refer to hybrid trout, 

 half-bred sheep, and mulattoes. 



APPLICATION TO EVOLUTION THEORY. 

 Like Weismannism, which has for one of its 

 foundations the idea of germinal continuity, 

 Mendelism conceives of the hereditary relation 

 in the strict sense, i. e. not as between the 

 bodies of parent and offspring, but between 

 the parental and the filial germ-cells. 



Like Weismannism, which has for another 

 of its foundations the idea of determinants 

 or representative particles constituting the 

 mosaic of inheritance, Mendelism regards the 

 organism as built up of a number of definite, 

 separably heritable characters. 



Mendelism has thrown light on at least 

 certain kinds of variation, those which are 

 due to the addition or omission of one or more 

 definite elements. As Bateson puts it : 

 " With the development of the inquiry it has 

 become clear that variation, in so far as it 

 consists in the omission of elementary factors, 

 is the consequence of a process of ' unpacking.' 

 The white sweet pea was created in the 

 variation by which one of the colour-factors 

 was dropped out. Such variation is not, as 



