1899] THE SCOPE OF NATURAL SELECTION 187 
between accommodations which are the direct result of environ- 
mental influence, just as wood becomes altered in its composition by a 
sufficient amount of heat, and those other forms of accommodations 
which are the result of the organismal response to its environment, and 
I pointed out that only in the former set of conditions was it strictly 
correct to speak of acquired modifications, and further that this 
somatic responsiveness was not in the least discordant with the 
principle of selection—it would, in fact, aid selectional development 
making the process of evolution more rapid. Now just as the 
chemical analogy tells against climatic modification, and in favour of 
use-development or organismal response with elimination of the less 
responsive, so I hope to show in this concluding portion of the paper 
that every broad generalisation tells against climatic modification, and 
in favour of organismal response, and I shall endeavour to show that 
the somatic response becomes increasingly separated off from the 
germinal, not through any special isolation of the germinal products, 
but for precisely similar reasons as other organs have become separated, 
namely, by increasing specialisation and complexity of structure.’ In 
this concluding portion, therefore, of the article, I wish to keep these 
distinctions constantly in view :—(1) The direct climatic response, an 
external influence or influences producing internal modifications ; 
except in so far as these external forces are destructive, I believe this 
influence to be negligible. (2) The response of the organism whether 
it be uni- or multicellular to external conditions and alterations that 
will ensue through elimination of the less fitted and preservation of 
the more fitted, internal response to external conditions, and external 
elimination of the less responsive organisms. (3) The relation, if 
any, that the somatic response bears to germinal variability. 
In considering the chief differences between plants and animals, 
we find certain more or less constant conditions which lead to the 
conclusion that protoplasm is not directly modifiable; thus a broad 
general difference is found between these two great divisions of the 
living world in the fact that vegetable organisms live on simpler foods 
than animal. The fact that the fungi and certain insectivorous plants 
form a partial exception to this rule, only increases the strength 
of the selectionist position, for, from the fact that the vast majority of 
the various forms of vegetable life do live on simpler foods than 
animal, we may infer that the difference in the structure of the 
protoplasm was not easily overcome, while the constancy of the 
character of the exceptions now that a change has been produced is 
almost positive proof that if organisms can be directly modified by 
climatic action it must be to a very slight degree. The same line of 
argument applies to the other differences observable between plants 
and animals. On the assumption that this difference of metabolism 
1 Lloyd Morgan, in his ‘‘ Animal Life and Intelligence,” has put forward a theory of 
reproductive specialisation to which I am greatly indebted. 
