42 ON THE ORIGIN OF SPECIES 



dwarfed condition of shells in the brackish waters of 

 the Baltic, or dwarfed 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 

 frequently to appear in the offspring from the 

 same parents, or which may be presumed to have thus 

 arisen, from being frequently observed in the indivi- 

 duals 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 differences are highly important for 

 us, as they afford materials for natural selection to 

 accumulate, in the same manner as man can accumu- 

 late in any given direction individual differences in his 

 domesticated productions. These individual differences 

 generally affect what naturalists 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 classificatory point of 

 view, sometimes vary in the individuals 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 varia- 

 bility 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 

 by slow degrees : yet quite recently Mr. Lubbock has 

 shown a degree of variability in these main nerves 



