2i6 Experime7ital 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 

 de-fimte 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 



^ 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. 



