60 ORIGIN OF SPECIES 



portant 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, some- 

 times vary in the individuals of the same species. I am con- 

 vinced that the most experienced naturalist would be sur- 

 prised at the number of the cases of variability, even in im- 

 portant 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 being 

 pleased at finding variability in important characters, and that 

 there are not many men who will laboriously examine inter- 

 nal and important organs, and compare them in many speci- 

 mens of the same species. It would never have been expected 

 that the branching of the main nerves close to the great cen- 

 tral ganglion of an insect would have been variable in the 

 same species ; it might have been thought that changes of 

 this nature could have been effected only by slow degrees; 

 yet Sir J. Lubbock has shown a degree of variability in these 

 main nerves in Coccus, which may almost be compared to the 

 irregular branching of the stem of a tree. This philosoph- 

 ical naturalist, I may add, has also shown that the muscles in 

 the larvae of certain insects are far from uniform. Authors 

 sometimes argue in a circle when they state that important 

 organs never vary; for these same authors practically rank 

 those parts as important (as some few naturalists have hon- 

 estly confessed) which do not vary; and, under this point of 

 view, no instance will ever be found of an important part 

 varying; but under any other point of view many instances 

 assuredly can be given. 



There is one point connected with individual differences, 

 which is extremely perplexing : I refer to those genera which 

 have been called "protean" or "polymorphic," in which the 

 species present an inordinate amount of variation. With re- 

 spect to many of these forms, hardly two naturalists agree 

 whether to rank them as species or as varieties. We may 

 instance Rubus, Rosa, and Hieracium amongst plants, several 

 genera of insects and of Brachiopod shells. In most poly- 

 morphic genera some of the species have fixed and definite 

 characters. Genera which are polymorphic in one country 

 seem to be, with a few exceptions, polymorphic in other coun- 



