1890 PEOFESSOE WEISMANN'S THEOEY 245 



that can happen in the lifetime of the individual 

 exercises any influence on its progeny; effects of use 

 or disuse, for example, cannot be inherited, nor, there- 

 fore, can any adaptation to external conditions which 

 are brought about in individual organisms. Natural 

 selection thus can only operate in spontaneous varia- 

 tions of germ-plasm, choosing those variations which, 

 when ' writ large ' in the resulting organisms, are best 

 suited to survive and transmit. 



This is the most important question that has 

 been raised in biology since I can remember, and one 

 proof of an inherited mutilation would settle the 

 matter against Weismann's theory. I am therefore 

 also trying the mutilation of caterpillars at the Zoo, 

 in the hope that a mutilation during what is virtually 

 an embryonic period of life will be most likely to be 

 transmitted, seeing that congenital variations are so 

 readily transmissible, and that these are changes of 

 a pre-embryonic kind. 



All well and with much love, yours ever, 



Geoege. 



Have you got the ' Contemporary Eeview ' for 

 June with my article on Darwinism ? If not, I will 

 send it. 



In a letter of which only a part has been kept, 

 Mr. Waggett tried to show how mutual sterility {i.e. 

 the production of sterile offspring) might be produced 

 between two parts of a species (so as to constitute 

 them two species), ' by way of natural selection,' 

 if only the small variations in every direction were 

 supposed which natural selection requires in respect 



