Chap. II. VARIATION 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 



