176 Cunningham's Theory of Evolution 



ment of such feminine organs as the milk glands, and 

 plays an important part in keeping latent masculine 

 characters in abeyance. As we have seen, when the 

 ovary is removed from a duck, she puts on the drake's 

 plumage. 



Mr. Cunningham believes that new characters in 

 animals have arisen in one of two ways. They may 

 be expressions of changes in the germ-cells (in the 

 "factors" or "genes" of the nuclear chromosomes) ; 

 or they may be due to bodily modifications induced 

 by extrinsic changes in environment and function. 

 This is the old contrast between "variations" in the 

 strict sense and bodily "modifications," between Weis- 

 mann's "blastogenic" changes and his "somatogenic" 

 changes. It is, in easier words, the contrast between 

 expressions and imprints, between outcomes and in- 

 dents. According to Mr. Cunningham, however, all 

 adaptive characters (structural fitnesses for par- 

 ticular uses and surroundings) have arisen from 

 bodily modifications, while non-adaptive characters 

 are due to "spontaneous" changes in the germ-cells. 



According to Mr. Cunningham, "no character 

 whose development is dependent in greater or less 

 degree on the stimulation of some substance derived 

 from the gonads can have originated as a mutation, 

 because the term mutation means a new character 

 which develops in the soma as the result of the loss or 

 gain of some new factor or determinant in the 

 chromosomes." But the argument in support of this 

 important conclusion appears to us little more than 

 assertive. There is surely no difficulty in supposing 



