OF THE MALAYAN REGION. 11 



It occurs in species of wide range, when groups of individuals have become partially- 

 isolated in several points of its area of distribution, in each of which a characteristic 

 form has become segregated more or less completely. Such forms are very common in 

 all parts of the world, and have often been classed as varieties or species alternately. I 

 restrict the term to those cases where the difference of the forms is very slight, or where 

 the segregation is more or less imperfect. The best example in the present group is 

 Pajiilio Agamemnon, L., a species which ranges over the greater part of tropical Asia, 

 the, whole of the Malay archipelago, and a portion of the Australian and Pacific regions. 

 The modifications are principally of size and form, and, though slight, are tolerably con- 

 stant in each locality. The steps, however, are so numerous and gradual that it would 

 be impossible to define many of them, though the extreme forms are sufficiently distinct. 

 FapiUo Sarjiedon, L., presents somewhat similar but less numerous variations. 



4. Coexwting variety. — This is a somewhat doubtful case. It is when a slight but per- 

 manent and hereditary modification of form exists in company with the parent or typical 

 form, without presenting those intermediate gradations which would constitute it a case 

 of simple variability. It is evidently only by direct evidence of the two forms breeding 

 separately that this can be distinguished from cUmorphism. The difficulty occurs in Pa- 

 pilio Jason, Esp., and P. Evemon, Bd., which inhabit the same localities, and are almost 

 exactly alike in form, size, and coloration, excej)t that the latter always wants a veiy 

 conspicuous red spot on the under surface, which is found not only in P. Jason, but in all 

 the allied species. It is only by breeding the two insects that it can be determined whe- 

 ther this is a case of a coexisting variety or of dimorphism. In the former case, however, 

 the difference being constant and so very conspicuous and easily defined, I see not how 

 we coiild escape considering it as a distinct species. A true case of coexisting forms 

 would, I consider, be produced, if a slight variety had become fixed as a local form, and 

 afterwards been brought into contact with the parent species with little or no inter- 

 mixture of the two ; and such instances do very probably occur. 



5. Race, or subspecies. — These are local forms completely fixed and isolated ; and there 

 is no possible test but individual opinion to determine which of them shall be considered 

 as species and which varieties. If stability of form and " the constant transmission of 

 some characteristic pecttliarity 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 Ulysses, P. Peranthus, P. Codrus, P. Eurypilus, P. Melenus, &c., are excellent 

 examples ; for while some present great and well-marked, others offer slight and incon- 

 spicuous 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 Hne. 

 The races of Papilio Ulysses, L., for example, vary in amount of modification from the 

 scarcely differing New Guinea form to those of Woodlark Island and New Caledonia, but 



white BOfiii living with yellow, red, and black women, and their offspring always reproducing the same types ; so that 

 at the end of many generations the men would remain pure white, and the women of the same well-marked races as 

 at the commencement. 



