441 
“ It is notorious, and we shall immediately adduce proofs, that 
increased use or action strengthens muscles, glands, sense- 
organs, &c. ; and that disuse, on the other hand, weakens them. 
I have not met with any clear explanation of this fact in works on 
physiology.”—(The Variation, vol. ii., p. 2QJ.) 
He denies that in some cases the principle of inherited 
effect of habit comes into action, and we may note here 
three reasons which are given for this view. He contends 
that mere habit may have done nothing towards the 
acclimatisation of the fruit trees of North America, be 
cause a multitude of seedlings are annually raised in that 
country, and none of them would succeed unless born 
with a fitting constitution.* That, in short, is to say that 
the direct effect of climate may have nothing to do with 
the acclimatisation, because Natural Selection may secure 
the survival of those which happened to be born with 
stronger constitutions. But it is not a question of what 
may be, but what actually is. 
Again, Mr. Darwin argues :— 
“ Under free nature we have no standard of comparison by which 
to judge of the effects of long-continued use or disuse, for we know 
not the parent forms.”—(Origin of Species, p. 108.) 
But in some cases we do undoubtedly know the parent 
forms. We know the year in which man has introduced 
certain animals into certain countries ; we know what they 
were when he took them there ; we know what they are 
now ; and, in some cases, we know how greatly they have 
been changed when they have been permitted to run wild. 
It is also argued that habits change while structures 
remain unmodified. That may take place sometimes, but 
it certainly does not take place universally. We have to 
account for the fixity of species as well as the transmu 
* The Variation, vol. ii., p. 312.