VARIATION UNDER NATURE 81 



some botanists as species, and he lias entirely omitted 

 several highly polymorphic genera. Under genera, in- 

 cluding the most polymorphic forms, Mr. Babington gives 

 251 species, whereas Mr. Bentham gives only 112 — a 

 difference of 139 doubtful forms! Among 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 spe- 

 cies, and by another as varieties, or, as they are often 

 called, geographical races! Mr. Wallace, in several valu- 

 able papers on the various animals, especially on the 

 Lepidoptera, inhabiting the islands of the great Malay 

 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 

 the limits of the same island. The local forms are mod* 

 erately 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 sufficiently dis- 

 tinct. The geographical races or sub-species are local 

 forms completely fixed and isolated; but as they do not 

 differ from each other by strongly marked and important 

 characters, "there is no possible test but individual opin- 

 ion to determine which of them shall be considered as 

 species and which as varieties." Lastly, representative 



