account. For no Sanguineous animal if it be divided into more parts

can live for any appreciable length of time, nor can it enjoy the

power of locomotion which it possessed while it was a continuous and

undivided whole. But some bloodless animals and polypods can live a

long time, if divided, in each of the severed parts, and can move in

the same way as before they were dismembered. Examples are what is

termed the centipede and other insects that are long in shape, for

even the hinder portion of all these goes on progressing in the same

direction as before when they are cut in two.

The explanation of their living when thus divided is that each of

them is constructed like a continuous body of many separate living

beings. It is plain, too, from what was said above why they are like

this. Animals constructed most naturally are made to move at two or

four points, and even limbless Sanguinea are no exception. They too

move by dint of four points, whereby they achieve progression. They go

forward by means of two flexions. For in each of their flexions

there is a right and a left, both before and behind in their flat

surface, in the part towards the head a right and a left front

point, and in the part towards the tail the two hinder points. They

look as if they moved at two points only, where they touch before

and behind, but that is only because they are narrow in breadth. Even.

in them the right is the sovereign part, and there is an alternate

correspondence behind, exactly as in quadrupeds. The reason of their

flexions is their great length, for just as tall men walk with their

spines bellied (undulated) forward, and when their right shoulder is

leading in a forward direction their left hip rather inclined

backwards, so that their middle becomes hollow and bellied

(undulated), so we ought to conceive snakes as moving in concave

curves (undulations) upon the ground. And this is evidence that they

move themselves like the quadrupeds, for they make the concave in

its turn convex and the convex concave. When in its turn the left of

the forward parts is leading, the concavity is in its turn reversed,