Seite - 60 - in The Origin of Species

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- estlyconfessed) 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-