The proportions of the leg and feet and the number of the scutellae 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.[35] _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.