Aristotle On Youth and Old Age,On Life and Death,On Breathing-Part 2

2All perfectly formed animals are to be divided into three parts, onethat by which food is taken in, one that by which excrement isdischarged, and the third the region intermediate between them. In thelargest animals this latter is called the chest and in the otherssomething corresponding; in some also it is more distinctly marked offthan in others. All those also that are capable of progression haveadditional members subservient to this purpose, by means of which theybear the whole trunk, to wit legs and feet and whatever parts arepossessed of the same powers. Now it is evident both by observationand by inference that the source of the nutritive soul is in the midstof the three parts. For many animals, when either part-the head or thereceptacle of the food-is cut off, retain life in that member to whichthe middle remains attached. This can be seen to occur in manyinsects, e.g. wasps and bees, and many animals also besides insectscan, though divided, continue to live by means of the part connectedwith nutrition.While this member is indeed in actuality single, yet potentiallyit is multiple, for these animals have a constitution similar tothat of Plants; plants when cut into sections continue to live, anda number of trees can be derived from one single source. A separateaccount will be given of the reason why some plants cannot live whendivided, while others can be propagated by the taking of slips. Inthis respect, however, plants and insects are alike.It is true that the nutritive soul, in beings possessing it, whileactually single must be potentially plural. And it is too with theprinciple of sensation, for evidently the divided segments of theseanimals have sensation. They are unable, however, to preserve theirconstitution, as plants can, not possessing the organs on which thecontinuance of life depends, for some lack the means for seizing,others for receiving their food; or again they may be destitute ofother organs as well.Divisible animals are like a number of animals grown together, butanimals of superior construction behave differently because theirconstitution is a unity of the highest possible kind. Hence some ofthe organs on division display slight sensitiveness because theyretain some psychical susceptibility; the animals continue to moveafter the vitals have been abstracted: tortoises, for example, do soeven after the heart has been removed.