﻿218 Darwin, and after Darwin. 



oyster, altered their manner of growth, and formed 

 prominent diverging rays." This is most probably due 

 to some change of food. So likewise may be the even 

 more remarkable case of Helix nemoralis, which was 

 introduced from Europe to Virginia a few years ago. 

 Under the new conditions it varied to such an extent 

 that up to last year no less than 125 varieties had 

 been discovered. Of these 6j, or more than half, 

 are new — that is, unknown in the native continent ot 

 the species 1 . 



In the case of Birds, the Brazilian parrot Chrysotis 

 festiva changes the green in its feathers to red or 

 yellow, if fed on the fat of certain fishes ; and the 

 Indian Lori has its splendid colouring preserved by 

 a peculiar kind of food (Wallace). The Bullfinch 

 is well known to turn black when fed on hemp 

 seeds, and the Canary to become red when fed on 

 cayenne pepper (Darwin). Starting from these facts, 

 Dr. Sauermann has recently investigated the subject 

 experimentally ; and finds that not only finches, but 

 likewise other birds, such as fowls, and pigeons, are 

 subject to similar variations of colour when fed on 

 cayenne pepper ; but in all cases the effect is pro- 

 duced only if the pepper is given to the young birds 

 before their first moult. Moreover, he finds that 

 a moist atmosphere facilitates the change of colour, 

 and that the ruddy hue is discharged under the 

 influence either of sunlight or of cold. Lastly, he 

 has observed that sundry other materials such as 

 glycerine and aniline dyes, produce the same results ; 

 so there can be no doubt that organic compounds 

 probably occur in nature which are capable of 

 1 Cockerell, Nature, vol. xli. p. 393. 



