PRESIDENTIAL ADDRESS. 47 



alteration in the germ-plasm of the reproductive cells, for"I have 

 always asserted that these changes, and these alone must be 

 transmitted (p. 410) ... In what other way could the trans 

 formation of species be produced, if changes in the germ-plasm 

 cannot be transmitted ? And how could the germ-plasm be 

 changed except by the operation of external influences, using 

 the words in their widest sense? " (p. 411). 



Now if, as he insists, external influences cannot possibly af 

 fect the germs of metazoans, and if, as he here maintains, it is 

 external influence alone that can influence any germs, it must 

 follow that the only variation that could have taken place in 

 the germ-plasms of the highest animals are those which oc 

 curred in the protozoan stage of their development. 



This is clearly a reductio ad absurdum, derived entirely from 

 his own statements, some of them among his latest utterances. 

 The difficulty is to see why he should adhere so tenaciously to 

 the idea that the germ-cells cannot be influenced by functional 

 changes in the organism containing them. The mere fact that 

 they are lodged within the body of an animal does not affect 

 the question unless it can be shown that they are so lodged that 

 no change is possible in the nature of their immediate surround 

 ings. To assume this is gratuitous and contrary to what would 

 be naturally supposed. In reading certain passages in his own 

 book one is strongly tempted to doubt whether he believes it 

 himself. For example, he says in one place speaking of hered 

 itary variations : " I believe however that they can be referred 

 to the various external influences to which the germ is exposed 

 before the commencement of embryonic development. Hence 

 we may fairly attribute to the adult organism influences which 

 determine the phyletic development of its descendants. For 

 the germ-cells are contained in the organism, and the external 

 influences which affect them are intimately connected with the 



