Weismannism tip to date (1893). 135 



[congenital] variation depends upon two factors ; 

 the one is the variability of the germ x and of its 

 progeny ; the other is that of all kinds of external 

 circumstances, in determining which out of many 

 competing germs, of nearly equal suitability, shall be 

 the one that becomes developed. The variability 

 of germs under changed conditions, and that of their 

 progeny, may be small, but it is indubitable ; absolute 

 uniformity being scarcely conceivable in the condition 

 and growth, and, therefore, in the reproduction of any 

 organism. The law of heredity goes no further than 

 to say, that like tends to produce like ; the tendency 

 may be very strong, but it cannot be absolute 2 ." 



Here, of course, there is a wide difference between 

 stirp and germ-plasm. For while Galton does not 

 entertain amphimixis among the "factors" of con- 

 genital variation, Weismann, as we are now well 

 aware, has hitherto regarded it as the sole cause 

 of such variation. Nevertheless, as we shall presently 

 find, Weismann has now greatly modified his views 

 upon this point, and does entertain, in The Germ-plasm, 

 both the " factors " mentioned by Galton. Hence, the 

 difference between the two theories in question with 

 regard to this matter is not nearly so wide as it was 

 prior to the publication of Weismann's last work. 



The next most important point of difference 

 between the theories of stirp and germ-plasm has 

 reference to the mechanism of ontogeny. According 

 to Galton, this is simply a struggle between all the 



1 By " germ " Galton means a carrier of heredity, which is capable 

 of self-multiplication. In these fundamental respects, therefore, it is 

 equivalent to a "gemmule" on the one hand and a "determinant" on 

 the other. The three terms are so far synonymous. 



2 Loc. cit., p. 338. 



