950 The American Naturalist. [November, 
lection are where organisms are restored to an environment 
which some of their ancestors experienced. We can then im- 
agine that the adaptive response to the old environment is 
something which has never been lost as in the well known 
reappearance of the pigment in flounders. 
It may be urged against the Morgan, Baldwin, Poulton 
views that the remarkable powers of self-adaptation, which, in 
many cases are favorable to the survival of the individual, are 
in many cases decidedly detrimental to the race, as where a 
maimed or mutilated embryo by regeneration reaches an adult 
or reproductive stage. It is obvious that reproduction from 
imperfect individuals would be decidedly detrimental, yet 
from the view taken by the above authors such reproduction 
would be necessary to secure the power of plastic modification 
for the race. 
It is certain, that at the present time, one of the surest and 
most attractive fields of inductive research, leading towards 
the discovery of the additional factors of evolution or what I 
have elsewhere called “the unknown factor,” is in experi- 
mental embryology and experimental zoology. If we could 
formulate the laws of self-adaptation or plastic modification 
we would be decidedly nearer the truth. It appears that Or- 
ganic Selection is a real process, but it has not yet been dem- 
onstrated that the powers of self-adaptation which become 
hereditary are only accumulated by selection. They may pos- 
sibly be accumulated by the inheritance of acquired modifica- 
tions as Lamarck supposed. 
Furthermore, another difficulty which I find with the com- 
pleteness of the Organic Selection hypothesis is identical with 
that which almost from the outset made me hesitate in regard 
to the completeness of the Lamarckian hypothesis, namely, 
many structures, such as the teeth, which exhibit no power of 
self-adaptation or plastic modification during life, which are, 
in fact, rendered decidedly less effective instead of more effect- 
ive by use and habit—these structures, I repeat, show precisely 
the same determinate and definite variation and consequent 
evolution as that which is exhibited in plastic and self-adapuve 
structures. This being the case, it is clear that “ Organic Selec- 
