42 DOUBTFUL SPECIES. 



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 ! 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 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 differ- 

 ences are seen to be so slight and graduated that it is impos- 

 sible to define or describe them, though at the same time 

 the extreme forms are sufficiently distinct. The geograph- 

 ical 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 opinion to determine which of 

 them shall be considered as species and which as varieties." 

 Lastly, representative species fill the same place in the nat- 

 ural economy of each island as do the local forms and sub- 

 species ; but as they are distinguished from each other by a 

 greater amount of difference than that between the local 

 forms and sub-species, they are almost universally ranked 

 by naturalists as true species. Nevertheless, no certain cri- 

 terion can possibly be given by which variable forms, local 

 forms, sub-species, and representative species can be recog- 

 nized. 



Many years ago, when comparing, and seeing others com- 

 pare, the birds from the closely neighboring islands of the 

 Galapagos Archipelago, one with another, and with those 



