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 characteristie 
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 
restriet 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 
Papilio 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. 
Papilio Sarpedon, L., presents somewhat similar but less numerous variations. 
4. Coexisting 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 dimorphism. 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, except that the latter always wants a very 
conspieuous red spot on the under surface, which is found not only in P. Jason, but in all 
the allied species. 1t 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 could 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 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 distinet and limited areas, must be regarded 
as a species; and as such I have in most cases treated them. The various modifications of 
Papilio Ulysses, P. Peranthus, P. Codrus, P. Eurypilus, P. Helenus, &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 line. 
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 men 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. 
ij c 2 
