ks daily swarming with a fresh supply of small
mollusca and crustacea. Exactly the same laws will apply to mammals.
Wild cats are prolific and have few enemies; why then are they never as
abundant as rabbits? The only intelligible answer is, that their supply
of food is more precarious. It appears evident, therefore, that so long
as a country remains physically unchanged, the numbers of its animal
population cannot materially increase. If one species does so, some
others requiring the same kind of food must diminish in proportion. The
numbers that die annually must be immense; and as the individual
existence of each animal depends upon itself, those that die must be
the weakest--the very young, the aged, and the diseased--while those
that prolong their existence can only be the most perfect in health and
vigour--those who are best able to obtain food regularly, and avoid
their numerous enemies. It is, as we commenced by remarking, "a struggle
for existence," in which the weakest and least perfectly organized must
always succumb.

_The Abundance or Rarity of a Species dependent upon its more or less
perfect Adaptation to the Conditions of Existence._

It seems evident that what takes place among the individuals of a
species must also occur among the several allied species of a
group,--viz., that those which are best adapted to obtain a regular
supply of food, and to defend themselves against the attacks of their
enemies and the vicissitudes of the seasons, must necessarily obtain and
preserve a superiority in population; while those species which from
some defect of power or organization are the least capable of
counteracting the vicissitudes of food-supply, &c., must diminish in
numbers, and, in extreme cases, become altogether extinct. Between these
extremes the species will present various degrees of capacity for
ensuring the means of preserving life; and it is thus we account for the
abundance or rarity of species. Our ignorance will generally prevent us
from accurately tracing the effects to their causes; but could we become
perfectly acquainted with the organization and habits of the various
species of animals, and could we measure the capacity of each for
performing the different acts necessary to its safety and existence
under all the varying circumstances by which it is surrounded, we might
be able even to calculate the proportionate abundance of individuals
which is the necessary result.

If now we have su