270 DEFINITE ACTION OF THE Chap. XXIII. 



u yellow colour, and on being plucked out, it is said, grow again of 

 " the same colour without any fresh operation.'' 



Bechstein 41 does not entertain any doubt that seclusion from 

 light affects, at least temporarily, the colours of cage-birds. 



It is well known that the shells of land-mollusca are affected by 

 the abundance of lime in different districts. Isidore Geoffroy Saint- 

 Hilaire i2 gives the case of Helix lactea, which has recently been 

 carried from Spain to the South of France and to the Rio Plata, and 

 in both countries now presents a distinct appearance, but whether 

 this has resulted from food or climate is not known. TVith respect 

 to the common oyster, Mr. F. Buckland informs me that he can 

 generally distinguish the shells from different districts; young 

 oysters brought from Wales and laid down in beds where " natives " 

 are indigenous, in the short space of two months begin to assume 

 the "native" character. M. Costa 43 has recorded a much more re- 

 markable case of the same nature, namely, that young shells taken 

 from the shores of England and placed in the Mediterranean, at 

 once altered their manner of growth and formed prominent diverging 

 rays, like those on the shells of the proper Mediterranean oyster. The 

 same individual shell, showing both forms of growth, was exhibited 

 before a society in Paris. Lastly, it is well known that caterpillars 

 fed on different food sometimes either themselves acquire a different 

 colour or produce moths differiug in colour. 44 



It would be travelling beyond my proper limits here to discuss 

 how far organic beings in a state of nature are definitely modified 

 by changed conditions. In my 'Origin of Species' I have given a 

 brief abstract of the facts bearing on this point, and have shown the 

 influence of light on the colours of birds, and of residence near the 

 sea on tlie lurid tints of insects, and on the succulency of plants. 

 Mr. Herbert Spencer 46 has recently discussed with much ability 

 this whole subject on general grounds. He argues, for instance, 

 that with all animals the external and internal tissues are differently 

 acta d on by the surrounding conditions, and they invariably differ 

 in intimate structure. - gain the upper and lower surfaces of 

 true leaves, as well as of steins and petioles, when these assume 



41 ' Naturgeschichtc dei Stuben- la Soc. Imp. d'Acclimat./ torn. viii. p. 



vogel,' 1840, s. 262 - 563. Fur analogous facts from 



4 - • HDt. Nat Gen.,' torn. iii. p. Dahlbom on Hymenoptera, see Wesfc- 



402. wood's • Modern Class, of Insects.' vol. 



4J ' Dull, de la Soc. Imp. d'Accli- ii. p. 98. See also Dr. L. Moller, 



mat.,' torn. ▼iii. p. 351. 'Die Abhiingigkeit der Insecteii.' 



S an account of Mr. Gregson's l*'i7. s. 70. 



iments on the Abcaxus <jru±?u- 4i "The Principles of Biology,' vol. 



. • Proa Entomolog. Soc.,' Jan. ii., 1866. The present chapters were 



• :e>e experiments have written before I had read Mr. Her- 



ofirmed by Mr. Greening, in bert Spencer's work, so that I have 



• Proa of the Northern Entomolog. not been able to make so much u<e of 



Soc.,* July 28th, 1862. Forthe effects it as I should otherwise probably 



iterpillars. se t a curious have done, 

 account by M. Michely, in ' Dull, de 



