160 THE MALAYAN PAPILIONIDE AS 
5. Race or subspecies—These are local forms com- 
pletely 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 sta- 
bility 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 Papilio Ulysses, P. Peran- 
thus, P. Codrus, P. Eurypilus, P. Helenus, d&c., are 
excellent examples; for while some present great and 
well-marked, others offer slight and inconspicuous dif- 
ferences, 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, for example, vary in amount of modification 
from the scarcely differing New Guinea form to those 
of Woodlark Island and New 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. Autolycus. 
We thus get 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 
differing in various amounts, each apparently constant. 
