III.] INDEPENDENT SIMILARITIES OF STRUCTURE. 95 



Ulysses has the blue colour obscured by dull and dusky 

 tints ; white in the closely allied species from the surround- 

 ing islands, the females are of almost as brilliant an azure 

 blue as the males. A parallel case to this is the occurrence, 

 in the small islands of Goram, Matabello, Ke, and Am, of 

 several distinct species of Euploea and Diadema, having 

 broad bands or patches of white, which do not exist in 

 any of the allied species from the larger islands. These 

 facts seem to indicate some local influence in modifying 

 colour, as unintelligible and almost as remarkable as that 

 which has resulted in the modifications of form previously 

 described." 



After endeavouring to explain some of the facts in a 

 way to be noticed directly, Mr. Wallace adds : 1 " But even 

 the conjectural explanation now given fails us in the 

 other cases of local modification. Why the species of the 

 Western Islands should be smaller than those further 

 east; why those of Amboyna should exceed in size those 

 of Gilolo and New Guinea ; why the tailed species of India 

 should begin to lose that appendage in the islands, and 

 retain no trace of it on the borders of the Pacific; and 

 why, in three separate cases, the females of Arnboyna 

 species should be less gaily attired than the corresponding 

 females of the surrounding islands, are questions which we 

 cannot at present attempt to answer. That they depend, 

 however, on some general principle is certain, because 

 analogous facts have been observed in other parts of the 

 world. Mr. Bates informs 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 



1 "Natural Selection," p. 177. 



