And God created great sea creatures, and every living thing that moves, which the waters brought forth abundantly, after their kind, and every winged fowl after its kind: and God saw that it was good.
All Commentaries on Genesis 1:21 Go To Genesis 1
Ambrose of Milan
The Word of God permeates every creature in the constitution of the world. Hence, as God had ordained, all kinds of living creatures were quickly produced from the earth. In compliance with a fixed law they all succeed each other from age to age according to their aspect and kind. The lion generates a lion; the tiger, a tiger; the ox, an ox; the swan, a swan; and the eagle, an eagle. What was once enjoined became in nature a habit for all time. Hence the earth has not ceased to offer the homage of its service. The original species of living creatures is reproduced for future ages by successive generations of its kind. .