40 Weismann evades a dilemma 



its discontinuity from body-plasm. In the 

 same year, H. P. Osborn^ had said: "If 

 acquired variations are transmitted there 

 must be some unknown principle in heredity, 

 if they are not transmitted there must be 

 some unknown factor in evolution." "A 

 perfectly correct conclusion" Weismann at 

 once replied, and set to work to find the new 

 factor by the simple method of extending 

 the range of natural selection to the ultimate 

 constituents of the germ-plasm itself He 

 supposed that the drama of the world without 

 is here repeated on a minute scale. The 

 determinants or ultimate constituents of the 

 germ-plasm struggle with each other for 

 nutriment. Some at length succumb and 

 the successful survivors are thus "selected." 

 So variations arise within the germ itself, 



1 In a lecture entitled The Hereditary Mechanism and the 

 Search for the Unknown Factors of Evolution. 



