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COMPARATIVE ANATOMY. 259
of the mechanical instincts of animals, which may be used,
together with the preceding one on Teleology, to complete
the whole examination of this subject in the present chapter.
Now, if we enter more closely into the above-mentioned
fitness of every animal s organisation for its mode of life
and means of subsistence, the question that first presents
itself is, whether that mode of life has been adapted to the
organisation, or vice versa. At first sight, the former as
sumption would seem to be the more correct one ;
since,
in Time, the organisation precedes the mode of life, and
the animal is thought to have adopted the mode of
existence for which its structure was best suited, making
the best use of the organs it found within itself : thus, for
instance, we think that the bird flies because it has wings,
and that the ox butts because it has horns ;
not conversely.
This view is shared by Lucretius (always an ominous sign
for an opinion) :
"
Nil ideo quoniam natum est in corpore, ut uti
l
Possemus ; sed, quod natum est, id procreat us urn."
Only this assumption does not explain how, collectively, the
quite different parts of an animal s organism so exactly
how no organ interferes with
correspond to its way of life ;
another, each rather assisting the others and none re
maining unemployed; also that no subordinate organ
would be better suited to another mode of existence, while
the life which the animal really leads is determined by the
principal organs alone, but, on the contrary, each part of
the animal not only corresponds to every other part, but
also to its mode of life: its claws, for instance, are in
variably adapted for seizing the prey which its teeth are
suited to tear and break, and its intestinal canal to digest :
its limbs are constructed to convey it where that prey is to
be found, and no organ ever remains unemployed. The
1 This is expanded, vol. iy. pp. 825-843.