VARIATION UNDER NATURE 37 



variety of another, not because the intermediate links have actually 

 been found, but because analogy leads the observer to suppose 

 either that they do now somewhere exist, or may formerly have 

 existed; and here a wide door for the entry of doubt and conjec- 

 ture is opened. 



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

 species or a variety, the opinion of naturalists having 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 assist- 

 ance 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 poly- 

 morphic 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 natu- 

 ralist as undoubted species, 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 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 moder- 

 ately 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 suf- 



