GENETICS 95 



and just as obviously the degree of pigmentation 

 which it brings about is conditioned among whites 

 by the environment. Butterflies of the wet- and 

 dry- season forms inherit the capacity to develop 

 into either, but actually develop according to the 

 conditioning environment. ^^ There are many cases 

 of this kind; in fact, all individual responses are 

 included. They have not been shown to affect the 

 chromosomes, for they are not transmitted in the 

 usual sense. 



A peculiar attitude has grown out of this situa- 

 tion. The gene, according to experimental evi- 

 dence, shows an astonishing degree of stability. 

 When it changes, it does so without evident ex- 

 ternal influence except in the irradiation experi- 

 ments referred to, and these influences appear 

 merely to hasten the occurrence of that which 

 would have occurred in due course of time. All 

 experiments in which apparent modification of 

 genes has occurred in connection with ordinary 

 individual responses to environment unfortunately 

 lend themselves to more or less destructive interpre- 

 tation, and in the most favorable cases the possi- 

 bility exists of the influences involved actually 

 reaching the chromosomes of the germ cells and 

 acting upon them directly. But a constant material 

 and constant conditions cannot give different re- 



16 Dixey, F. A., Proc. S. Lond. Ent. & Nat. Hist. Soc, 1916-1917, p. 11. 

 1916, cites experiments performed by Marshall. 



