Heredity and the Origin of Variations. 163 



criticism. Nor do I think that mutilations are likely to 

 afford the right sort of evidence one way or the other. We 

 must look to less abnormal influences. What we require 

 is evidence in favour of or against the supposition that 

 modijications of the body-cells are transmitted to the germ- 

 cells. Now, these modifications must clearly be of such a 

 nature as to be receivable by the cells without in any way 

 •destroying their integrity. The destruction or removal of 

 •cells is something very different from this. If it were 

 proved that mutilations are inherited, this would not 

 necessarily show that normal cell-modifications are trans- 

 missible. And if the evidence in favour of inherited 

 mutilations breaks down, as I believe it does, this does not 

 show that more normal modifications such as those with 

 which we are familiar, as occurring in the course of indi- 

 vidual life, are not capable of transmission. I repeat, we 

 must not look to mutilations for evidence for or against the 

 supposition that acquired characters are inherited. We 

 must look to less abnormal influences. 



These readily divide themselves into two classes. The 

 first includes the direct effects on the organism of the 

 environment — effects, for example, wrought by changes of 

 climate, alteration of the medium in which the organism 

 lives, and so forth. The second comprises the effects of 

 use and disuse — the changes in the organism wrought by 

 the exercise of function. 



Taking the former first, we have the remarkable case of 

 Saturnia, which was communicated to Darwin by Moritz 

 Wagner. Mr. Mivart thus summarizes it: "A number of 

 pupsB were brought, in 1870, to Switzerland from Texas of 

 a species of Saturnia, widely different from European 



I species. In May, 1871, the moths developed out of the 

 cocoons (which had spent the winter in Switzerland), and 

 resembled entirely the Texan species. Their young were 

 fed on leaves of Juglans regia (the Texan form feeding on 

 Juglans nigra), and they changed into moths so different, 

 !not only in colour, but also in form, from their parents, 

 ihat they were reckoned by entomologists as a distinct 

 ! 



