4 MR. A. R. WALLACE ON THE PAPILIONIDÆ 
sometimes even straying into the narrow bazaars or covered markets of the city. In 
Java the golden-dusted Arjuna may often be seen at damp places on the roadside in the 
mountain districts, in company with Sarpedon, Bathycles, and Agamemnon, and less fre- 
quently the beautiful swallow-tailed Antiphates. In the more luxuriant parts of these 
islands one can hardly take a morning’s walk in the neighbourhood of a town or village 
without seeing three or four species of Papilio, and often twice that number. No less 
than 120 species of the family are now known to inhabit the Archipelago, and of these 
ninety-six were collected by myself. Twenty-nine species are found in Borneo, being the 
largest number in any one island, twenty-three species having been obtained by myself 
in the vicinity of Sarawak; Java has twenty-seven species; Celebes and the Peninsula 
of Malaeca twenty-three each. Further east the numbers decrease, Batchian producing 
seventeen, and New Guinea only thirteen, though this number is certainly too small, 
owing to our present imperfect knowledge of that great island. 
In estimating these numbers I have had the usual difficulty to encounter, of determining 
what to consider species and what varieties. The Malayan region, consisting of a large 
number of islands of generally great antiquity, possesses, compared to its actual area, a 
great number of distinct forms, often indeed distinguished by very slight characters, but 
in most cases so constant in large series of specimens, and so easily separable from each 
other, that I know not on what principle we can refuse to give them the name and rank 
of species. One of the best and most orthodox definitions is that of Pritehard, the great 
ethnologist, who says, that “ separate origin and distinctness of race, evinced by a con- 
stant transmission of some characteristic peculiarity of organization," constitutes a species. 
Now leaving out the question of * origin," which we cannot determine, and taking only 
the proof of separate origin, “ the constant transmission of some characteristic peculiarity 
of organization," we have a definition which will compel us to neglect altogether the 
amount of difference between any two forms, and to consider only whether the differences 
that present themselves are permanent. The rule, therefore, I have endeavoured to adopt 
is, that when the difference between two forms inhabiting separate areas seems quite 
constant, when it can be defined in words, and when it is not confined to a single pecu- 
liarity only, I have considered such forms to be species. When, however, the individuals 
of each locality vary among themselves, so as to cause the distinctions between the two 
forms to become inconsiderable and indefinite, or where the differences, though constant, 
are confined to one particular only, such as size, tint, or a single point of difference in 
marking or in outline, I class one of the forms as à variety of the other. 
I find as a general rule that the constancy of species is in an inverse ratio to their range. 
Those which are confined to one or two islands are generally very constant. When they 
extend to many islands, considerable variability appears ; 
sive range over a large part of the Archipelago, 
large. These facts are explicable on Mr. Dar 
over a wide area, it must have had 
‚ and, were they completely isolated, would soon 
his process is checked by the dispersive powers 
