96 THE GENESIS OF PECIES. [CHAP. 



also that the J^neas group of Papilios never have tails 

 in the equatorial regions and the Amazon valley, but 

 gradually acquire tails in many cases as they range 

 towards the northern or southern tropic. Even in Europe 

 we have somewhat similar facts, for the species and 

 varieties of butterflies peculiar to the Island of Sardinia 

 are generally smaller and more deeply coloured than those 

 of the mainland, and the same has been recently showr 

 to be the case with the common tortoiseshell butterfly in 

 the Isle of Man ; while Papilio Hospiton, peculiar to the 

 former island, has lost the tail, which is a prominent 

 feature of the closely allied P. Machaon" 



" Facts of a similar nature to those now brought forward 

 would no doubt be found to occur in other groups of insects, 

 were local faunas carefully studied in relation to those of 

 the surrounding countries ; and they seem to indicate that 

 climate and other physical causes have, in some cases, a 

 very powerful effect in modifying specific form and colour, 

 and thus directly aid in producing the endless variety of 

 nature." 



With regard to butterflies of Celebes belonging to 

 different families, they present "a peculiarity of outline 

 which distinguishes them at a glance from those of any 

 other part of the world : " 1 it is that the upper wings are 

 generally more elongated and the anterior margin more 

 curved. Moreover, there is, in most instances, near the 

 base an abrupt bend or elbow, which in some species is 

 very conspicuous. Mr. Wallace endeavours to explain 

 this phenomenon by the supposed presence at some time 

 of special persecutors of the modified forms, supporting 

 the opinion by the remark that small, obscure, very 



1 "Malay Archipelago," vol. i. p. 439. 



