1891.] Are Acquired Variations Inherited ? 307 
seed, and are therefore the consequences of variations in the germ. 
The fact that such variations zever occur in the first generation 
proves that they must be prepared for by a gradual transforma- 
tion of the germ-plasm. . . It is therefore possible that the 
modifying effects of external influences upon the germ-plasm may 
be gradual, and may increase in the course of generations so that 
visible changes in the body (soma) are not reached until the effects 
have reached a certain intensity.” 
The best-attested instances of the action of Environment in 
producing special characters are those seen in its action upon the 
reproductive organs. A slight change of conditions sometimes 
produces sterility, as seen in the cases of “isolation” and “ diver- 
gence” advanced by Gulick ,and Romanes. , Here the best 
explanation seems to be that the environment has acted directly 
upon the germ-cells. This could only be proved, however, by 
experiments in artificial impregnation, for it is possible that the 
cause of sterility might lie in some of the somatic functions 
accessory to impregnation or intercourse. A second instance of 
this kind is the effect of nutrition in the determination of sex, as 
proved by the experiments of Yung and Giron,” and employed as- 
one of the main principles in the two theories of Heredity 
advanced respectively by Ryder and Geddes. 
It is not necessary to enumerate the many well-known cases of 
rapid response to new environment by modifications, which we 
must analyze somewhat differently. Among the best recorded 
are those of Saturnia (imported to Switzerland from Texas),® and 
Artemia“ Now it is a very important fact that the modifications 
observed in such cases are in the main adaptive,—that is, in course 
of a very few generations not only are the organisms thoroughly 
acclimated, but they develop substantially new adaptive characters. 
We can readily understand how the germ-plasm might respond 
i les by high nutrition from 56 
pt ie Oe sa man ce or ot 
when poorly fed, only 40 per cent. See Geddes and Thompson, “ Evolution of Sex, 
Chap. LV. x 
