called STATION, which means--given the climate, the particular kind of
place in which an animal or a plant lives or grows; for example, the
station of a fish is in the water, of a fresh-water fish in fresh
water; the station of a marine fish is in the sea, and a marine animal
may have a station higher or deeper. So again with land animals: the
differences in their stations are those of different soils and
neighbourhoods; some being best adapted to a calcareous, and others to
an arenaceous soil. The third condition of existence is FOOD, by which
I mean food in the broadest sense, the supply of the materials necessary
to the existence of an organic being; in the case of a plant the
inorganic matters, such as carbonic acid, water, ammonia, and the
earthy salts or salines; in the case of the animal the inorganic and
organic matters, which we have seen they require; then these are all,
at least the two first, what we may call the inorganic or physical
conditions of existence. Food takes a mid-place, and then come the
organic conditions; by which I mean the conditions which depend upon the
state of the rest of the organic creation, upon the number and kind of
living beings, with which an animal is surrounded. You may class these
under two heads: there are organic beings, which operate as
'opponents', and there are organic beings which operate as 'helpers' to
any given organic creature. The opponents may be of two kinds: there
are the 'indirect opponents', which are what we may call 'rivals'; and
there are the 'direct opponents', those which strive to destroy the
creature; and these we call 'enemies'. By rivals I mean, of course, in
the case of plants, those which require for their support the same kind
of soil and station, and, among animals, those which require the same
kind of station, or food, or climate; those are the indirect opponents;
the direct opponents are, of course, those which prey upon an animal or
vegetable. The 'helpers' may also be regarded as direct and indirect:
in the case of a carnivorous animal, for example, a particular