And God said,
Let the waters bring forth abundantly the moving creature that has life, and fowl that may fly above the earth in the open firmament of heaven.
All Commentaries on Genesis 1:20 Go To Genesis 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.
The creeping creature having life: Nature passes from one extreme to another through the medium; and therefore there are creatures of intermediate type between the animals of the air and those of the water, having something in common with both; and they are reckoned as belonging to that class to which they are most allied, through the characters possessed in common with that class, rather than with the other. But in order to include among fishes all such intermediate forms as have special characters like to theirs, the words, "Let the waters bring forth the creeping creature having life," are followed by these: "God created great whales," etc.
And the fowl that may fly over the earth under the firmament of heaven: But birds move in the lower part of the air, and so are said to fly "beneath the firmament," even if the firmament be taken to mean the region of clouds.