94 DARWINISM chap. 



of the scntellpe also vary. The eggs also varj' somcAvhat in 

 size and shape ; and the amount of downy clothing on the 

 young bird, "svhen first hatched, differs very considerably. 

 Finally, the attitude of the body, the manner of walking, the 

 mode of flight, and the voice, all exhibit modifications of the 

 most remarkable kind.^ 



AccUmaiisation. 



A very important kind of variation is that constitutional 

 change termed acclimatisation, which enables any organism to 

 become gradually adapted to a different climate from the 

 parent stock. As closely allied species often inhabit different 

 countries possessing very different climates, we should expect 

 to find cases illustrating this change among our domesticated 

 animals and cultivated plants, A few examples will therefore 

 be adduced showinf;- that such constitutional variation does 

 occur. 



Among animals the cases are not numerous, because no 

 systematic attempt has been made to select varieties for this 

 special quality. It has, however, been observed that, though 

 no European dogs thrive well in India, the Newfoundland dog, 

 originating from a severe climate, can hardly be kept alive. 

 A better case, perhaps, is fm^nished by merino sheep, w^hich, 

 when imported directly from England, do not thrive, Avhile those 

 Avhich have been bred in the intermediate climate of the Cape 

 of Good Hope do much better. When geese w^ere first intro- 

 duced into Bogota, they laid feAv eggs at long intervals, and 

 few of the young sur\dved. By degrees, hoAvever, the fecundity 

 improved, and in about twenty years became equal to what 

 it is in Europe. According to Garcilaso, Avhen fowls AA^ere 

 first introduced into Peru they Avere not fertile, AA^hereas now 

 they are as much so as in Europe. 



Plants furnish much more important eAddence. Our 

 nurserymen distinguish in their catalogues varieties of fruit- 

 trees Avhich are more or less hardy, and this is especially the 

 case in America, Avhere certain varieties only will stand the 

 severe climate of Canada. There is one variety of pear, the 

 Forelle, Avhich both in England and France Avithstood frosts 



^ This account of domestic pigeons is greatly condensed from Mr. 

 Darwin's work already refen-ed to. 



