On The Motion Of Animals   

but also within those things which move in place, and initiate their

own movement. For one part of an animal must be moved, and another

be at rest, and against this the part which is moved will support

itself and be moved; for example, if it move one of its parts; for one

part, as it were, supports itself against another part at rest.

But about things without life which are moved one might ask the

question whether all contain in themselves both that which is at

rest and that which initiates movement, and whether they also, for

instance fire, earth, or any other inanimate thing, must support

themselves against something outside which is at rest. Or is this

impossible and must it not be looked for rather in those primary

causes by which they are set in motion? For all things without life

are moved by something other, and the origin of all things so moved

are things which move themselves. And out of these we have spoken

about animals (for they must all have in themselves that which is at

rest, and without them that against which they are supported); but

whether there is some higher and prime mover is not clear, and an

origin of that kind involves a different discussion. Animals at any

rate which move themselves are all moved supporting themselves on what

is outside them, even when they inspire and expire; for there is no

essential difference between casting a great and a small weight, and

this is what men do when they spit and cough and when they breathe

in and breathe out.

5



But is it only in that which moves itself in place that there must

be a point at rest, or does this hold also of that which causes its

own qualitative changes, and its own growth? Now the question of

original generation and decay is different; for if there is, as we

hold, a primary movement, this would be the cause of generation and

decay, and probably of all the secondary movements too. And as in

the universe, so in the animal world this is the primary movement,