GEOGRAPHICAL DISTRIBUTION. 133 
under the action of agents to -which they are unaccus- 
tomed, and which tend to their gradual extinction. 
The omnivorous hog, which accompanies man in all 
his migrations, seeks them out in their most secluded 
retreats, and uproots them from the soil itself; and 
the domestic poultry find in them a favorite food. 
Fires, which from year to year are applied to consume 
the trees felled by the axe, aid in the work ; and finally 
comes the plough, which completes their extermina- 
tion. Thus, they mostly disappear as the settlement 
of the country proceeds, until in the older and most 
populous districts, they are nearly extinct or are repre- 
sented only by the smaller species, existing under fa- 
vorable circumstances, and in the most retired local- 
ities. So, too, in the well-wooded regions of the West 
not actually subjected to the operations of agriculture, 
where they were until lately known to be very nume- 
rous, the universal practice of rearing great numbers 
of hogs, which roam at large in the forest, has dimin- 
ished their numbers and rendered them much less com- 
mon. No species, however, is likely to become extinct 
from this cause alone, for many escape these various 
dangers, and some portions of land remain uncultivated : 
and when suffered to rest for a time unmolested, they 
increase very rapidly. 
Destruction by Animals. The increase of individuals 
is kept in check by the depredations of other species 
of the same family, and even by other individuals of 
the same species. Other kinds of animals also prey 
vol. 1. 35 
