144 THE MALAYAN PAPILIONID& AS 



3rd, local forms ; 4th, co-existing varieties ; 5th, races 

 or subspecies ; and 6th, true species. 



1. Simple variability. Under this head I include all 

 those cases in which the specific form is to some extent 

 unstable. Throughout the whole range of the species, 

 and even in the progeny of individuals, there occur 

 continual and uncertain differences of form, analogous 

 to that variability which is so characteristic of domestic 

 breeds. It is impossible usefully to define any of these 

 forms, because there are indefinite gradations to each 

 other form. Species which possess these characteristics 

 have always a wide range, and are more frequently the 

 inhabitants of continents than of islands, though such 

 cases are always exceptional, it being far more common 

 for specific forms to be fixed within very narrow limits 

 of variation. The only good example of this kind of 

 variability which occurs among the Malayan Papilio- 

 nida3 is in Papilio Severus, a species inhabiting all the 

 islands of the Moluccas and New Guinea, and exhibit- 

 ing in each of them a greater amount of individual 

 difference than often serves to distinguish well - 

 marked species. Almost equally remarkable are the 

 variations exhibited in most of the species of Ornithop- 

 tera, which I have found in some cases to extend even 

 to the form of the wing and the arrangement of the 

 nervures. Closely allied, however, to these variable 

 species are others which, though differing slightly from 

 them, are constant and confined to limited areas. After 

 satisfying oneself, by the examination of numerous 

 specimens captured in their native countries, that the 



