On Youth And Old Age, On Life And Death, On Breathing   

expel it in order to prevent its being swallowed simultaneously with

the food. Thus crustaceans, like the Carcini and Carabi, discharge

water through the folds beside their shaggy parts, while cuttlefish

and the polyps employ for this purpose the hollow above the head.

There is, however, a more precise account of these in the History of

Animals.

Thus it has been explained that the cause of the admission of the

water is refrigeration, and the fact that animals constituted for a

life in water must feed in it.



19



An account must next be given of refrigeration and the manner in

which it occurs in respiring animals and those possessed of gills.

We have already said that all animals with lungs respire. The reason

why some creatures have this organ, and why those having it need

respiration, is that the higher animals have a greater proportion of

heat, for at the same time they must have been assigned a higher

soul and they have a higher nature than plants. Hence too those with

most blood and most warmth in the lung are of greater size, and animal

in which the blood in the lung is purest and most plentiful is the

most erect, namely man; and the reason why he alone has his upper part

directed to the upper part of the universe is that he possesses such a

lung. Hence this organ as much as any other must be assigned to the

essence of the animal both in man and in other cases.

This then is the purpose of refrigeration. As for the constraining

and efficient cause, we must believe that it created animals like

this, just as it created many others also not of this constitution.

For some have a greater proportion of earth in their composition, like

plants, and others, e.g. aquatic animals, contain a larger amount of

water; while winged and terrestrial animals have an excess of air

and fire respectively. It is always in the region proper to the