17 '-! THE MALAYAN PAP1LIONID1E 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- 

 lionidse and Pieridse) 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 a priori evidence in favour 

 of an identity of the causes that have produced such 



