94 
DARWINISM 
CHAP. 
of the scutellfe also vary. The eggs also vary somewhat in 
size and shape ; and the amount of downy clothing on the 
young bird, when 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. 1 
Acclimatisation. 
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 showing 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 furnished by merino sheep, which, 
when imported directly from England, do not thrive, while those 
which have been bred in the intermediate climate of the Cape 
of Good Hope do much better. When geese were first intro¬ 
duced into Bogota, they laid few eggs at long intervals, and 
few of the young survived. By degrees, however, the fecundity 
improved, and in about twenty years became equal to what 
it is in Europe. According to Garcilaso, when fowls were 
first introduced into Peru they were not fertile, whereas now 
they are as much so as in Europe. 
Plants furnish much more important evidence. Our 
nurserymen distinguish in their catalogues varieties of fruit- 
trees which are more or less hardy, and this is especially the 
case in America, where certain varieties only will stand the 
severe climate of Canada. There is one variety of pear, the 
Forelle, which both in England and France withstood frosts 
1 This account of domestic pigeons is greatly condensed from Mr. 
Darwin's work already referred to. 
