316 THE EFFECTS OF CONDITIONS 



As Wallace points out,* however, " it is an error to 

 assume that what seem to us identical conditions are 

 really identical to such small and delicate organisms as 

 these land molluscs." 



Upon Lepidoptera, we have seen in a previous chap- 

 ter that the effect of particular conditions of environ- 

 ment, such as temperature and nutrition, may be 

 considerable. One would imagine, therefore, that 

 changes in the conditions of life as a whole might form 

 an even more potent source of variation. Conclusive 

 evidence upon this point is, unfortunately, almost un- 

 obtainable, though of the inconclusive kind which forms 

 the larger part of this chapter there is plenty. For in- 

 stance, Wallace f came to the conclusion that, with 

 reference to the local forms occurring in the Indian and 

 Malayan regions, " larger or smaller districts, or even 

 single islands give a special character to the majority 

 of their Papilionidse. For instance : The species of the 

 Indian region (Sumatra, Java, and Borneo) are almost 

 invariably smaller than the allied species inhabiting 

 Celebes and the Moluccas. The species of New Guinea 

 and Australia are also, though in a less degree, smaller 

 than the nearest species or varieties of the Moluc- 

 cas. . . The species and varieties of Celebes possess a 

 striking character in the form of the anterior wings, 

 different from that of the allied species and varieties of 

 all the surrounding islands. Tailed species of India or 

 the Indian region become tailless as they spread east- 

 ward through the Archipelago; in Amboyna and Ceram 

 the females of several species are dull-coloured, while 



*" Darwinism," p. 148. 



t" Contributions to Natural Selection," p. 167, 1870. 



