III.] INDEPENDENT SIMILARITIES OF STRUCTURE. 99 



forms me that, in three distinct groups, Papilios, which, on 

 the Upper Amazon, and in most other parts of South 

 America, have spotless upper wings, obtain pale or white 

 spots at Para and on the Lower Amazon, and also that the 

 ^Eneas group of Papilios never have tails in the equatorial 

 regions and the Amazon valley, but gradually acquire tails in 

 many cases as they range toward 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 

 colored than those of the main-land, and the same has been 

 recently shown to be the case with the common tortoise- 

 shell 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 for- 

 ward 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 indi- 

 cate that climate and other physical causes have, in some 

 cases, a very powerful effect in modifying specific form and 

 color, and thus directly aid in producing the endless variety 

 of nature." 



With regard to butterflies of Celebes belonging to dif- 

 ferent families, they present " a peculiarity of outline which 

 distinguishes them at a glance from those of any other part 

 of the world : " IT 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 con- 

 spicuous. Mr. Wallace endeavors to explain this phenome- 

 non by the supposed presence at some time of special per- 

 secutors of the modified forms, supporting the opinion by 

 the remark that small, obscure, very rapidly flying and mim- 

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



