Phenomena of Variation cuid Geographiad Distribution. 175 



5. Race, or suhpecies. — These are local forms completely fixed and 

 isolated : and there is no possible test but individual opinion to deter- 

 mine which of them shall be considered as species, and which varieties. 

 If stability of form and "the constant transmission of some characteristic 

 peculiarity of organization " is the test of a species (and I can find no 

 other test that is more certain than individual opinion), then every 

 one of these fixed races, confined as they almost always are to distinct and 

 limited areas, must be regarded as a species ; and as such I have in 

 most cases treated them. The various modifications of Fapilio Ulys- 

 ses, P. Peranthus, P. Codnis, P. Eurypilus, P. Belenu.^, etc., are ex- 

 cellent examples ; for while some present great and well-marked, 

 others oflfer slight and inconspicuous differences, yet in all cases these 

 differences seem equally fixed and permanent. If, therefore, we call 

 some of these forms species, and others varieties, we introduce a purely 

 arbitrary distinction, and shall never be able to decide where to draw 

 the line. The races of Papilio Ulysses, L., for example, vary in 

 amount of modification from the scarcely difiering New Guinea form 

 to those of Woodlark Island and Xew Caledonia, but all seem equally 

 constant ; and as most of these had already been named and described 

 as species, I have added the New Guinea form under the name of P. 

 Penelope. Wie thus got a little group of Ulyssine Papilios, the whole 

 comprised within a very limited area, each one confined to a separate 

 portion of that area, and, though difiering in various amounts, each 

 apparently constant. Few naturalists will doubt that all these may 

 and probably have been derived from a common stock ; and therefore 

 it seems desirable that there should be a unity in our method of treat- 

 ing them : either call them all varieties or all species. Varieties, how- 

 ever, continually get overlooked ; in lists of species they are often alto- 

 gether unrecorded; and thus we are in danger of neglecting the inter- 

 esting phenomena of variation and distribution which they present. I 

 think it advisable, therefore, to name all such forms ; and those who 

 will not accept them as species may consider them as sub-species or 

 races. 



6. *%ec!'es.— Species are merely-those strongly marked races or local 

 forms which, when in contact, do not intermix, and when inhabiting 

 distinct areas are generally believed to have had a separate origin, and 

 to be incapable of producing a fertile hybrid offspring. But as the 

 test of hybridity can not be applied in one case in ten thousand, and 

 even if it could be applied, would prove nothing, since it is founded 

 on an assumption of the very question to be decided— and as the test 

 of separate origin is in every case inapplicable— and as, further, the 

 test of. non-intermixture is useless, except in those rare cases where 



