38 ON THE TENDENCY OF VARIETIES TO DEPART 
on a limited scale, yet, if applied to high numbers, 
the results come nearer to what theory demands, 
and, as we approach to an infinity of examples, 
become strictly accurate. Now the scale on which 
nature works is so vast—the numbers of individuals 
and the periods of time with which she deals ap- 
proach so near to infinity, than any cause, how- 
ever slight, and howéver liable to be veiled and 
counteracted by accidental circumstances, must in 
the end produce its full legitimate results. 
e 
The Partial Reversion of Domesticated Varieties 
explained. ' 
Let us now turn to domesticated animals, and in- 
quire how varieties produced among them are affected 
by the principles here enunciated. The essential 
difference in the condition .of wild and domestic 
animals is this,—that among the former, their well- 
being and very existence depend upon the full exer- 
cise and healthy condition of all their senses and 
physical ‘powers, whereas, among the latter, these are 
only partially exercised, and in some cases are abso-— 
lutely unused. A wild animal has to search, and 
often to labour, for every mouthful of food—to ex- 
ercise sight, hearing, and smell in seeking it, and 
in avoiding dangers, in procuring shelter from the 
inclemency of the seasons, and in providing for the 
subsistence and safety of its offspring. There is no 
muscle of its body that is not called into daily and 
hourly activity; there is no sense or faculty that is 
