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the fourth day corresponds to the first day on which he had said that the light was made, so on this fifth day he mentions the waters and the firmament of heaven to show that the fifth day corresponds to the second. It must, however, be observed that Augustine differs from other writers in his opinion about the production of fishes and birds, as he differs about the production of plants. For while others say that fishes and birds were produced on the fifth day actually, he holds that the nature of the waters produced them on that day potentially.
Reply Obj. 1: It was laid down by Avicenna that animals of all kinds can be generated by various minglings of the elements, and naturally, without any kind of seed. This, however, seems repugnant to the fact that nature produces its effects by determinate means, and consequently, those things that are naturally generated from seed cannot be generated naturally in any other way. It ought, then, rather to be said that in the natural generation of all animals that are generated from seed, the active principle lies in the formative power of the seed, but that in the case of animals generated from putrefaction, the formative power of is the influence of the heavenly bodies. The material principle, however, in the generation of either kind of animals, is either some element, or something compounded of the elements. But at the first beginning of the world the active principle was the Word of God, which produced animals from material elements, either in act, as some holy writers say, or virtually, as Augustine teaches. Not as though the power possessed by water or earth of producing all animals resides in the earth and the water themselves, as Avicenna held, but in the power originally given to the elements of producing them from elemental matter by the power of seed or the influence of the stars.
Reply Obj. 2: The bodies of birds and fishes may be considered from two