Chap. 11 , 
VAKIATIOK UNDER NATURE. 
45 
plants on Alpine summits, or the thicker fur of an 
animal from far northwards, would not in some cases be 
inherited for at least some few generations ? and in this 
case I presume that the form would be called a variety. 
Again, we have many slight differences which may be 
called individual differences, such as are known fre¬ 
quently to appear in the offspring from the same parents, 
or which may be presumed to have thus arisen, from 
being frequently observed in the individuals of the same 
species inhabiting the same confined locality. No one 
supposes that all the individuals of the same species are 
cast in the very same mould. These individual differ¬ 
ences are highly important for us, as they afford mate¬ 
rials for natural selection to accumulate, in the same 
manner as man can accumulate in any given direction 
individual differences in his domesticated productions. 
These individual differences generally affect what natu¬ 
ralists consider unimportant parts; but I could show by 
a long catalogue of facts, that parts which must be called 
important, whether viewed under a physiological or clas- 
sificatory point of view, sometimes vary in the indivi¬ 
duals of the same species. I am convinced that the most 
experienced naturalist would be surprised at the number 
of the cases of variability, even in important parts of 
structure, which he could collect on good authority, as I 
have collected, during a course of years. It should be 
remembered that systematists are far from pleased at 
finding variability in important characters, and that there 
are not many men who will laboriously examine internal 
and important organs, and compare them in many speci¬ 
mens of the same species. I should never have expected 
that the branching of the main nerves close to the great 
central ganglion of an insect would have been variable 
in the same species; I should have expected that 
changes of this nature could have been effected only 
