Ixviii 



Mr. Darwin himself founds his theory, in the first place, on the results 

 of domestication and cultivation ; but the objection felt to the evidences 

 of modification thus obtained — namely, that in domestication species 

 are placed under artificial conditions and yield results dissimilar to 

 those observed in free Nature — is not easy to overcome. In noting the 

 modification of species in their natural state, as accompanying the 

 differences of local conditions under which we find them, which is 

 what I mean by the facts of distribution, we see the operation of 

 changes independent of artificial interference ; and once admitting 

 that species do slowly and intermittently extend their areas of dis- 

 semination, and that certain local forms are modifications of their 

 sister-forms, the whole process of the formation of species by natural 

 means lies straightway open to our investigation, the steps of modifi- 

 cation being capable of proof, by logical induction, after the premisses 

 just mentioned are granted. Having attempted to follow this line of 

 investigation in the case of several species and groups of species of 

 insects, I have been surprisied to find how defective are most of our 

 collections in suites of specimens, and our books in recorded facts of 

 this nature. Few Entomologists lay themselves out to collect series 

 of specimens illustrative of this subject: I can assure them from 

 experience that they would find it most interesting to do so. It is not 

 sufficient to collect the varieties inhabiting a limited region, like the 

 British Isles, but to follow each species over the entire area of its dis- 

 tribution, both in a vertical and horizontal direction, i. e. up mountain 

 slopes, and over geographical areas, and obtain specimens from every 

 place where varieties occur. 



Another important memoir of similarly wide interest to the one just 

 discussed has been recently read in England. 1 mean one on the 

 mimetic butterflies of Southern Africa, by Mr. Roland Trimen, which 

 will shortly be published in the Transactions of the Linnean Society. 

 The process of adaptation of varieties of a species to different local 

 conditions, and their great modification, is here expounded in the genus 

 Papilio, especially in the remarkable case of Papilio Merope. The 

 females of this species have a tendency to vary greatly from their 

 males, and to put on a disguise which assimilates them to one or 

 other species of Danais. It is a truly wonderful fact that at the Cape 

 of Good Hope and in Western Tropical Africa, the females imitate 

 species of Danais widely different in coloration, the males all re- 

 maining unchanged or nearly so, whilst in Madagascar the female 



