58 DOUBTFUL SPECIES. [Chap. 11. 



as varieties, but which have all- been ranked by bota- 

 nists as species; and in inaking 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 351 species, whereas Mr. Bentham 

 gives only 113, — a difference 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 com- 

 mon in separated areas. How many of the birds and 

 insects in North America and Europe, which diffei 

 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 

 Malayan archipelago, shows that they may be classed 

 under four heads, namely, as variable forms, as local 

 forms, as geographical races or sub-species, and as true 

 representative species. The first or variable forms vary 

 much within the 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 differences are seen to be so 

 slight and graduated, that it is impossible to define or 

 describe them, though at the same time the extreme 

 forms are sufSciently distinct. The geographical racea 

 or sub-species are local forms completely fixed and iso- 

 lated; but as they do not differ from each other by 



