544 



TEE AMERICAN NATURALIST 



[Vol. LI 



duced by the hereditary genes— a single gene difference 

 turning the scale in this way or in that. In this case we 

 have, I think, an excellent illustration of the difference 

 between the mechanism of inheritance and the chemical 

 effects of genetic factors on development. Highly inter- 

 esting and important as it undoubtedly would be to work 

 out these connections, yet the evidence is very explicit in 

 showing that the distribution of the materials of heredity 

 during the maturation process of the egg and sperm is 

 different in kind from their action through the cytoplasm 

 on the developing organism. 



For purposes, then, of closer analysis, it seems desirable 

 in the present condition of genetics and embryology to 

 recognize that the mechanism of distribution of the hered- 

 itary units or genes is a process of an entirely different 

 kind from the effects that the genes produce through the 

 agency of the cytoplasm of the embryo. The activity of 

 the cytoplasm is, of course, bound up with the environ- 

 ment in which it takes place— a relation that is so intimate 

 that in most cases the (Constitution of the cytoplasm and 

 the nature of the environment in which it finds itself arc 

 studied as two sides of tlie same i)rob1em. It is true that 

 the iti('<-lviiii>in MciKU'liiui lici-cdity may also he affected 

 by tlic I'liviioiiiiicnt. certainly by the external environ- 

 by the cytoplasmic envii'ojiiiicnl >in('(' lir-iducs lias sliown 

 that the process is somcwli.-it tlitVciriii in young mid old 

 flies. Rut there is no evidence that the ndation of the 

 maturation process to the environment is in any way re- 

 lated to the reactions that go on between the cytoplasm of 

 the developing embryo and its environment, and it has 

 only led to confusion whcnevei' an attempt has been made 

 to dt'dnc ri-o„i The iiatniv ,.f the cinhi^niiic ivaction the 

 natui'c of the iiiecli;ini-in that di-tnhnte- the genes in 



