A parallel case to this is the occurrence, in the small islands of Goram, Matabello, Ke, and Aru, 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:[64] "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 {85} 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 Amboyna 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 also that the AEneas 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.