Chap. II.] DOUBTFUL SPECIES. 37 



the intermediate forms always remove the difficulty. In very many 

 cases, however, one form is ranked as a variety of another, not 

 because the intermediate links have actually been found, but 

 because analogy leads the observer to suppose either that they dc 

 now somewhere exist, or may formerly have existed ; and here a 

 wide door for the entry of doubt and conjecture is opened. 



Hence, in determining whether a form should be ranked as a 

 species or a variety, the opinion of naturalists havmg sound judg- 

 ment and wide experience seems the only guide to follow. We 

 must, however, in many cases, decide by a majority of naturalists, 

 for few well-marked and well-known varieties can be named which 

 have not been ranked as species by at least some competent 

 judges. 



That varieties of this doubtful nature are far from uncommon 

 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 arc 

 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 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 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 Lepi- 

 doptera, inhabiting the islands of the great Malayan archipelago, 

 shows that they may be classed under four heads, namely, as vari- 

 able 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 dif- 



