338 STUDIES, SCIENTIFIC AND SOCIAL 



Individual Modification. 



The question of purely individual modification by use 

 or environment requires further consideration, because, 

 owing to the unhesitating acceptance of the inheritance 

 of acquired characters by Darwin and most contemporary 

 naturalists, the important bearing of facts proving the 

 effect of external conditions on individuals has been, and 

 still is, altogether overlooked. Two cases in particular 

 are continually quoted by the advocates of inheritance, 

 as if they were in some way antagonistic to Weismann's 

 theory, whereas they really support that theory, and 

 almost prove it. The first is that of the Texan species of 

 Saturnia (Emperor-moth) which feeds on the black walnut 

 {Jnglans nigra), and which, when pupae were brought to 

 Switzerland and the larvae raised from the eggs laid by 

 the moth were fed on the common walnut {Jnglans regia), 

 produced moths which differed so much from the parent 

 both in colour and form that it appeared to be a new 

 species. Darwin, writing to Wagner of this case, says: 

 " When I wrote the Origin, and for some years afterwards, 

 I could find little good evidence of the direct action of the 

 environment ; now there is a large body of evidence, and 

 your case of the Saturnia is one of the most remarkable 

 of which I have heard." In referring to this letter, 

 Professor H. F. Osborn, in one of the most intelligent 

 discussions of this question I have yet seen from an 

 American author, says, " Darwin distinctly abandoned the 

 utility principle in the case of Saturnia " ; ^ and Mr. D. G. 

 Elliott, in his presidential address to the American 

 Ornithologists' Union in 1891, quoted the same case as 

 affording striking evidence of the transmission of acquired 

 modifications. 



Professor Lloyd Morgan (in his Animal Life and 

 Intelligence, pp. 163 — 166) sees clearly that this and other 

 cases do not prove more than a modification of the 

 individual ; but it seems to me to go further than this. 



^ Are Acquired Variations Inherited? An Argument, by Henry 

 Fairfield Osborn, in The American Naturalist, February, 1891. 



