Chap. XXIII. CONDITIONS OF LIFE. 269 



domesticated quadrupeds can be distinguished from those of wild 

 animals by the state of their surface and general appearance. It is 

 scarcely possible to read Nathusius's excellent ' Vorstudien,' 38 and 

 doubt that, with the highly improved races of the pig, abundant 

 food has produced a conspicuous effect on the general form of the 

 body, on the breadth of the head and face, and even on the teeth. 

 Nathusius rests much on the case of a purely bred Berkshire pig, 

 which when two months old became diseased in its digestive organs, 

 and was preserved for observation until nineteen months old ; at 

 this age it had lost several characteristic features of the breed, and 

 had acquired a long, narrow head, of large size relatively to its 

 small body, and elongated legs. But in this case and in some others 

 we ought not to assume that, because certain characters are lost, 

 perhaps through reversion, under one course of treatment, therefore 

 that they were at first directly produced by an opposite treatment. 



In the case of the rabbit, which has become feral on the island of 

 Porto Santo, we are at first strongly tempted to attribute the 

 whole change — the greatly reduced size, the altered tints of the fur, 

 and the loss of certain characteristic marks — to the definite action 

 of the new conditions to which it has been exposed. But in all such 

 cases we have to consider in addition the tendency to reversion to 

 progenitors more or less remote, and the natural selection of the 

 finest shades of difference. 



The nature of the food sometimes either definitely induces certain 

 peculiarities, or stands in some close relation with them. Pallas 

 long ago asserted that the fat-tailed sheep of Siberia degenerate 

 and. lose their enormous tails when removed from certain saline 

 pastures ; and recently Erman 39 states that this occurs with the 

 Kirgisian sheep when brought to Orenburgh. 



It is well known that heinp-seecl causes bullfinches and certain 

 other birds to become black. Mr. Wallace has communicated to me 

 some much more remarkable facts of the same nature. The natives 

 of the Amazonian region feed the common green parrot (Chn/sotis 

 /estiva, Linn.) with the fat of large Siluroid fishes, and the birds 

 thus treated become beautifully variegated with red and yellow 

 feathers. In the Malayan archipelago, the natives of Gilolo alter in 

 an analogous manner the colours of another parrot, namely, the 

 Lorius garrulus, Linn., and thus produce the Lori rajah or King- 

 Lory. These parrots in the Malay Islands and South America, 

 when fed by the natives on natural vegetable food, such as rice and 

 plaintains, retain their proper colours. Mr. Wallace has, also, re- 

 corded 40 a still more singular fact. " The Indians (of S. America) 

 " have a curious art by which they change the colours of the feathers 

 " of many birds. They pluck out those from the part they wish to 

 " paint, and inoculate the fresh wound with the milky secretion 

 " from the skin of a small toad. The feathers grow of a brilliant 



35 ' Schweinesehadel,' 1864, s. 99. « A. R. Wallace, 'Travels on the 



39 'Travels in Siberia,' Eng. trans- Amazon and Rio Negro,' p. 29-i. 

 iat., vol. i. p. 228. 



