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On The Gait Of Animals   


A difficulty might perhaps be raised about birds. How, it may be

said, can they, either when they fly or when they walk, be said to

move at four points? Now we did not say that all Sanguinea move at

four points, but merely at not more than four. Moreover, they cannot

as a fact fly if their legs be removed, nor walk without their

wings. Even a man does not walk without moving his shoulders.

Everything indeed, as we have said, makes a change of place by flexion

and straightening, for all things progress by pressing upon what being

beneath them up to a point gives way as it were gradually;

accordingly, even if there be no flexion in another member, there must

be at least in the point whence motion begins, is in feathered

(flying) insects at the base of the 'scale-wing', in birds at the base

of the wing, in others at the base of the corresponding member, the

fins, for instance, in fish. In others, for example snakes, the

flexion begins in the joints of the body.

In winged creatures the tail serves, like a ship's rudder, to keep

the flying thing in its course. The tail then must like other limbs be

able to bend at the point of attachment. And so flying insects, and

birds (Schizoptera) whose tails are ill-adapted for the use in

question, for example peacocks, and domestic cocks, and generally

birds that hardly fly, cannot steer a straight course. Flying

insects have absolutely no tail, and so drift along like a

rudderless vessel, and beat against anything they happen upon; and

this applies equally to sharded insects, like the scarab-beetle and

the chafer, and to unsharded, like bees and wasps. Further, birds that

are not made for flight have a tail that is of no use; for instance

the purple coot and the heron and all water-fowl. These fly stretching

out their feet as a substitute for a tail, and use their legs

instead of a tail to direct their flight. The flight of insects is

slow and frail because the character of their feathery wings is not

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