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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 assumption 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 Possemus; sed, quod natum est, id procreat usum. l [Since indeed nothing originates in the body in order that we may use it, but what has originated is the cause of our using it]
Only this assumption does not explain how, collectively, the quite different parts of an animal's organism so exactly correspond to its way of life; how no organ interferes with another, each rather assisting the others and none remaining 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 invariably 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 in vol. iv. pp. 825-843.
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