[63] therefore He commanded all the races of fish and sea-monsters to stand together in their places, animals differing both in their sizes and in their qualities; for they vary in different seas, though in some cases they are the same, and every animal was not formed to live every where. And was not this reasonable? For some of them delight in marshy places, and in water which is very deep; and some in sewers and harbours, being neither able to crawl up upon the land, nor to swim off far from the land. Some, again, dwell in the middle and in the deep sea, and avoid all the projecting promontories and islands and rocks: some also exult in fine weather and in calms, and some in storms and heavy surf. For being exercised by continual buffetings, and being in the habit of withstanding the current by force, they are very vigorous and become stout.
After that he created the races of birds as akin to the races of aquatic animals (for they are each of them swimmers), leaving no species of creatures which traverse the air unfinished.