Chap. II. DOUBTFUL SPECIES. 57 



judgment and wide experience seems the only guide to follow. 

 itVe 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 uncom- 

 mon cannot be disputed. Compare the several floras of Great 

 Britain, of France, or of the United States, drawn up by dif- 

 ferent botanists, and see Avhat a surprising number of forms 

 have been ranked by one botanist as good species, and by an- 

 other as mere varieties. ^Ir. H. C. Watson, to whom I lie 

 inider deep obligation for assistance of all kinds, has marked 

 fur me 18"v British plants, which are generally considered as 

 varieties, but which have all been ranked by botanists as spe- 

 cies ; and in making this list he has omitted many trifling varie- 

 ties, but which nevertheless have been ranked by some bota- 

 nists as specie's, and he has entirely omitted several bighly-poly- 

 morj^hic genera. Under genera, including the most polymor- 

 {)hic forms, Mr. Babington gives 251 species, whereas Mr. 

 Benthara 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 those 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, as 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 sul)-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 eqch separate island; but when all 

 the forms from the several islands arc compared, 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 geographical 

 races or sul>speoies are local forms completely fixed and iso- 

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

 marked and important characters, " there is no possible test but 



