339 
closely related, for one part may be wholly suppressed or rendered 
monstrous without any other part of the body being affected.”—(The 
Variation, vol. ii., p. 31Q.) 
This looks like putting the cart before the horse. The 
general principle should surely be first announced, and 
then the exceptions or apparent exceptions should be 
stated. Mr. Darwin also urges the plea of ignorance in 
this case :— 
“ In cases of true correlated variation, we are sometimes able to see 
the nature of the connexion ; but in most cases the bond is hidden 
from us, and certainly differs in different cases. We can seldom say 
which of two correlated parts first varies and induces a change in the 
other, or whether the two are simultaneously produced by some 
distinct cause.”—(The Variation, vol. ii., p.320.) 
Remarks like these would in some connections require 
no comment. They are simply an honest expression of 
a present ignorance or of a very partial knowledge, and 
they produce the pleasing effect of suggesting the keen 
insight and perfect candour of the writer. But we must 
beware of giving such statements a different significance. 
Either correlated variation is a law of nature or not. If it 
is not, let us say so at once, and have no more to do with 
it. But if it is a law of nature, it will be as efficient as 
all other laws are ; and if we do not find the results which 
we anticipate, we may depend upon it that the reason is 
either because we are looking for results which we have no 
right to expect, or because some other law of nature 
is modifying the effect of this. So far as we are ignorant 
we are bound to remove that ignorance, if possible; but if 
not, we have no right to question the existence of a law 
whose action is in other connections manifest to all. 
The doubts thrown upon the efficacy of the principle of 
correlated variation assume a new significancy when we 
find that Mr. Darwin introduces the principle of Natural 
Selection into his very definitions of correlated variation ;