Organic Nature s Riddle 343 



^icus stipulata grown on a wall has small thin leaves, and 

 jlings to the surface like a large moss or a miniature ivy. 



*lanted out, it forms a shrub, with large, coarse, leathery 

 leaves. 



Mr. Wallace has pointed out some of the curious direct 

 [effects of external conditions on organisms. He tells us^ 

 ;that in the small island of Amboina the butterflies (twelve 

 [species, of nine different genera) are larger than those of 

 ^any of the more considerable islands about it, and that this 

 an effect probably due to some local influence. In Celebes 

 a whole series of butterflies are not only of a larger size, but 

 have the same peculiar form of wing. The Duke of York's 

 Island seems, he tells us, to have a tendency to make birds 

 and insects white, or at least pale, and the Philippines to 

 develop metallic colours ; while the Moluccas and New Guinea 

 seem to favour blackness and redness in parrots and pigeons. 

 Species of butterflies which in India are provided with a tail 

 to the wing begin to lose that appendage in the islands, and 

 retain no trace of it on the borders of the Pacific. The 

 iEneas group of papilios never have tails in the equatorial 

 region of the Amazon Valley, but gradually acquire tails, 

 in many cases, as they range towards the northern and 

 southern tropics. Mr. Gould says that birds are more 

 highly coloured under a clear atmosphere than in islands 

 or on coasts — a condition which also seems to affect insects, 

 while it is notorious that many shore plants have fleshy 

 leaves. We need but refer to the English oysters mentioned 

 by Costa, which, when transported to the Mediterranean, 

 grew rapidly hke the true Mediterranean oyster, and to the 

 twenty different kinds of American trees said by Mr. Meehan 

 to differ in the saTne manner from their nearest American 

 allies, as well as to the dogs, cats, and rabbits which have 

 been proved to undergo modifications directly induced by 



^ Tropical Nature, pp. 254-259. Before quoted ; see aiife, p. 202. 



