runners run faster if they swing their arms; there is in extending the

arms a kind of leaning against the hands and wrists. In all cases then

that which moves makes its change of position by the use of at least

two parts of the body; one part so to speak squeezes, the other is

squeezed; for the part that is still is squeezed as it has to carry

the weight, the part that is lifted strains against that which carries

the weight. It follows then that nothing without parts can move itself

in this way, for it has not in it the distinction of the part which is

passive and that which is active.

4



Again, the boundaries by which living beings are naturally

determined are six in number, superior and inferior, before and

behind, right and left. Of these all living beings have a superior and

an inferior part; for superior and inferior is in plants too, not only

in animals. And this distinction is one of function, not merely of

position relatively to our earth and the sky above our heads. The

superior is that from which flows in each kind the distribution of

nutriment and the process of growth; the inferior is that to which the

process flows and in which it ends. One is a starting-point, the other

an end, and the starting-point is the superior. And yet it might be

thought that in the case of plants at least the inferior is rather the

appropriate starting-point, for in them the superior and inferior

are in position other than in animals. Still they are similarly

situated from the point of view of function, though not in their

position relatively to the universe. The roots are the superior part

of a plant, for from them the nutriment is distributed to the

growing members, and a plant takes it with its roots as an animal does

with its mouth.

Things that are not only alive but are animals have both a front and

a back, because they all have sense, and front and back are

distinguished by reference to sense. The front is the part in which