Seite - 63 - in The Origin of Species

DOUBTFUL SPECIES 63 varieties can be named which have not been ranked as spe- cies by at least some competent judges. That varieties of this doubtful nature are far from un- common cannot be disputed. Compare the several floras of Great Britain, of France, or of the United States, drawn up by different botanists, and see what a surprising number of forms have been ranked by one botanist as good species, and by another as mere varieties. Mr. H. C. Watson, to whom I lie under deep obligation for assistance of all kinds, has marked for me 182 British plants, which are generally considered as varieties, but which have all been ranked by botanists as species; and in making this list he has omitted many trifling varieties, but which nevertheless have been ranked by some botanists as species, and he has entirely omitted several highly polymorphic genera. Under genera, including the most polymorphic forms, Mr. Babington gives 251 species, whereas Mr. Bentham gives only 112,—a differ- ence of 139 doubtful forms ! Amongst animals which unite for each birth, and which are highly locomotive, doubtful forms, ranked by one zoologist as a species and by another as a variety, can rarely be found within the same country, but are common in separated areas. How many of the birds and insects in North America and Europe, which differ very slightly from each other, have been ranked by one eminent naturalist as undoubted species, and by another as varieties, or, as they are often called, geographical races ! Mr. Wallace, in several valuable papers on the various animals, especially on the Lepidoptera, inhabiting the islands of the great Ma- layan archipelago, shows that they may be classed under four heads, namely, as variable forms, as local forms, as geo- graphical races or sub-species, and as true representative species. The first or variable forms vary much within tho limits of the same island. The local forms are moderately constant and distinct in each separate island; but when all from the several islands are compared together, the differ- ences are seen to be so slight and graduated, that it is im- possible to define or describe them, though at the same time the extreme forms are sufficiently distinct. The geo- graphical races or sub-species are local forms completely fixed and isolated; but as they do not differ from each other