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Whether any animal breathes air.
"And the types of animals, etc." Here one asks whether any animal breathes air.
1. It seems not, since respiration occurs for the sake of cooling the heart and lungs. But air is warm and moist, and water is cold and moist. Therefore a breathing animal needs to draw in water more than air.
2. In the same way, an animal drawing in water derives its life from the water; an indication of this is that if it should be out of the water, it dies immediately. But an animal cannot live on air; therefore it cannot take in air.
The Philosopher says the opposite.
One must say that some animals have a very hot heart. Nature gave these lungs, which are a sort of fan for the heart, and by their expansion air is drawn in and by their contraction it is expelled, as one sees in a fan or bellows. But in one way it is true that the heart is a particularly impassible member, for according to the Philosopher in the third book of On the Parts [of Animals], "it is not susceptible to weakness." Water and earth change things materially a great deal, and this is why neither water nor earth is drawn to cool the heart, because these things are particularly material. Neither is fire drawn there, for it would increase the heart's heat. But, on account of its thinness and conformity, air is drawn in. Those animals, however, that do not have a proper heart or lungs but rather have some material object comparable to the heart, as certain fish do, draw in water to cool it, just as those that do have lungs draw in air. And the Philosopher says this in the text that "some draw in air and expel air" and "some, like fish, draw in water and expel it through gills."
1. On to the arguments. To the first, one must reply that although air may be warm and moist, it nevertheless has less heat than the heart. And it is apparent that very hot water can be cooled by the infusion or admixture of tepid water. Additionally, the air in which we live is especially cold owing to the commingling of vapors and its proximity to earth and water.
2. To the second, one must reply that an animal that draws in water does not derive its life from this water, because "we are nourished by the same things upon which we exist," according to Aristotle in the book On Generation. So, since an animal is mixed, it is therefore necessary that its nourishment be mixed. Thus, those proposing that the chameleon and the mole, the herring and the salamander live on pure elements do not speak the truth, because nourishment has to be in a proximate disposition to the one to be nourished, and a simple [element] is not proximate in power to the mixed, but is remote from it. So fish do not live on sea water or on water alone, but on some mixture of water and earth.
Whether an aquatic animal, once its form is changed, can become terrestrial.
Next one asks whether an aquatic animal, once its form is changed, can become terrestrial.
1. It seems not. For it is said in the fourth book of the On Meteorology, in the old translation: "Let alchemists know that species cannot be transmuted, but altered." But there is no less diversity among animals than among metals, and therefore, etc.
2. Again, no transition occurs from one genus to another genus. But according to the Philosopher at the beginning of this book, fish and birds "differ in genus," and as a result one cannot pass into the other.
The Philosopher says the opposite.
One must reply that "animal" can be considered in two ways: either with respect to matter or with respect to form. If with respect to form, then one cannot be transmuted into another. For just as white does not become black, so one species of animal cannot be changed into another. If, however, we consider "animal" with respect to matter, then one can be changed into another. For it happens that the matter existing under one species has a great affinity to the matter of another species, and this is why, when the form of the one withdraws, the form of another can be introduced to the matter. This is evident in dead bodies, when vermin and hornets [ strabones] are generated from them. It is also evident in the generation of certain animals that occurs through an intermediary, as is apparent for frogs. For certain black animals with tails are generated from the semen of frogs that later, after they have cast off the tails, adopt feet, and whereas earlier they live in water, they later live on land. The reason, however, that an aquatic animal becomes terrestrial and not vice versa can be that the matter of the aquatic animal can be thickened by the coldness of the water so much that it becomes suited to the form of a terrestrial animal. But the longer it remains a terrestrial animal, the more it tends to dryness and as a consequence it becomes more removed from the nature of an aquatic animal.
1. On to the arguments. To the first, one must say that one species of metal never becomes another, even though by means of alchemy it can happen that one species appears as another. It is the same among animals: one species does not become another, although after one species another species can be introduced to the same matter.
2. To the second, one must reply that an aquatic animal, a walking animal, and a flying animal do not differ in genus, because there is not another genus contained under "animal." Nevertheless the Philosopher does say that "fish" and "bird" do differ in genus, because they differ in their general properties; for example, their movement occurs by means of various differences. It has been posited, then, that fish and bird differ in proximate genus [genus propinquum], yet they do not differ in the logical genus [ genus naturale] or in the predicamental genus [ genus praedicabile], because they agree in their matter and whatever agrees in matter cannot pass from one genus into another.
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