174 THE MALAYAN PAPILIONIDE AS 
Remarks on the facts of Local variation. 
The facts now brought forward seem to me of the 
highest interest. We see that almost all the species 
in two important families of the Lepidoptera (Papi- 
lionidee and Pieridee) acquire, in a single island, a 
characteristic modification of form distinguishing them 
from the allied species and varieties of all the sur- 
rounding islands. In other equally extensive families 
no such change occurs, except in one or two isolated 
species. However we may account for these pheno- 
mena, or whether we may be quite unable to account 
for them, they furnish, in my opinion, a strong cor- 
roborative testimony in favour of the doctrine of the 
origin of species by successive small variations; for 
we have here slight varieties, local races, and un- 
doubted species, all modified in exactly the same 
manner, indicating plainly a common cause producing 
identical results. On the generally received theory 
of the original distinctness and permanence of species, 
we are met by this difficulty: one portion of these 
curiously modified forms are admitted to have been 
produced by variation and some natural action of local 
conditions; whilst the other portion, differing from 
the former only in degree, and connected with them 
by insensible gradations, are said to have possessed 
this peculiarity of form at their first creation, or to 
have derived it from unknown causes of a totally dis- 
tinct nature. Is not the & priori evidence in favour 
of an identity of the causes that have produced such 
