VARIATION AND HEREDITY 137 



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 rela- 

 tion 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 fac- 

 tors, is the consequence of a process of 'un- 

 packing.' The white sweet pea was created 

 in the variation by which one of the colour- 

 factors was dropped out. Such variation is 

 not, as it was formerly supposed that all 

 variation must be, a progress from a lower 

 degree of complexity to a higher, but the 



