216 Experimental Zoology 
external conditions have slowly modified the forms, and the evi- 
dence for this view seems almost irresistible when we find that 
many animals and plants are distinctly modified when placed 
in a different environment, without, in most cases, however, 
transcending the limits of the variety or race. On the other 
hand, it is equally true that when brought back to the original 
environment the changed forms return in most cases to their 
former condition. In this respect they differ from wild species, 
from fixed varieties, and from elementary species, which remain 
true to their type under varying conditions, except for the tem- 
porary changes just mentioned. Therefore it does not seem 
probable that changes of this kind directly transformed one 
species into another. Suppose, however, that a new environ- 
ment may sometimes call forth in the germ-cells effects that are 
definite and inherited, — fixed, in other words, in the sense that 
the germ-cells are true to their kind, —then we can perhaps 
harmonize the apparently contradictory evidence. The new mu- 
tation thus induced might be, in some forms and under certain 
conditions, similar in kind to the effects produced on the body- 
cells. The results, however, would not be reached through 
the body-cells, but by independent, definite variation of the 
germ-cells, as a result of a new environment. Offspring from 
such germ-cells should remain true to their new kind when 
returned to the original environment unless the germ-cells are 
again affected; but whether a return to the original type would 
even then occur cannot be stated. Macdougal has recently 
made the important discovery that mutations may be induced 
by treating the germ-cells of the evening primrose with salt solu- 
tions. 
In other cases the new mutation or mutations may not be in 
the direction in which the body-cells are temporarily affected 
(if affected at all), but in some other direction or directions, and 
new types are formed bearing no relation to the former modifi- 
cations affected in the body-cells. That the new type may also 
1 This statement is somewhat arbitrary. It is intended to mean that with a 
return of the former conditions the new type returns to its original condition. 
