From Hexameron, Paradise, and Cain and Abel, Savage translation, 1961.

Book 5: The Fifth Day, chapter 1.2

And God also said : 'Let the waters abound with life and above the earth let winged creatures fly below the firmament of the heavens.' At this command the waters immediately poured forth their offspring. The rivers were in labor. The lakes produced their quota of life. The sea itself began to bear all manner of reptiles and to send forth according to its kind whatever was there created. The tiny creeks and the muddy marshes were not without exercising the power of creation granted to them. Fish leaped from the rivers. Dolphins frolicked in the waves. Shell-fish clung to the rocks. Oysters adhered to the depths and the sea-urchins waxed strong.

Book 5: The Fifth Day, chapter 2.5-6

Take note of the fact that there are far more animals in the sea than on land. Count, if you can, all the species of fish from the smallest to the greatest, for example, the cuttlefish, the polypus, the oyster, the sea and river crab, and even the different types among these. What shall I say of the different species of serpent, of the dragon, the murena, and the eel? not to mention the scorpions, the frogs, the tortoise, the mustela, also, and the sea-dog, the sea-calf, the monstrous shark, the dolphin, the seal, and the sea-lion. What need is there to add to our list the sea-ousel, the sea-thrush, and the sea-peacock, whose colors we see in the feathers of birds as, for example, the black ousel and the peacock with its varied colored back and neck; also in the feathers of the thrush with its spotted breast and in the feathers of the rest of the birds whose names and species belong to this earth of ours? These, as a matter of fact, came into existence in the seas and in the multitudinous rivers, since the waters at the divine command were the first to produce 'creeping creatures having life.' Add to this the beneficence of God whereby what we cherish in the water is an object of fear on land. This is true, because what is harmful on land is in water without harm - even the water-snakes are bereft of poison. The lion is a terrifying animal on land; he is gentle in the water. The murena, which is said to be somewhat harmful, is a choice table food. The frog is repellent when in the marshes, is pleasing when in water, and excels all in its deliciousness as food. If you desire to know more on this subject, make enquiry of fishermen in different localities, for no one person can possibly know all there is to know. ... What shall I say of the tender qualities of the ravens and wolves of the sea? These wolves do not inspire fear in lambs. Such is the charm of water that its sea-lions flee from the sea-calves, as follows from the prophetic utterance on the sanctity of the Church: 'Then the wolf and the lamb shall feed together, the lion and the ox shall eat straw.'

Book 5: The Fifth Day, chapter 3.9

Fish, therefore, know nothing of union with alien species. They do not have unnatural betrothals such as are designedly brought about between animals of two different species as, for instance, the donkey and the mare, or again the female ass and the horse, both being examples of unnatural union. Certainly there are cases in which nature suffers more in the nature of defilement rather than that of injury to the individual.

Book 5: The Fifth Day, chapter 14.44

After our description of the various fishes we have appropriately taken up next in order the subject of those birds that are also associated with water, in so far as they, too, in a similar fashion find pleasure in the art of swimming. Hence these birds seem to be primarily related to the fish species, since each has a certain element in common, that of being able to swim. The second elements which fishes and birds also share lies in the fact that the art of flying is an aspect of that of swimming. As a fish cuts through the water in the act of swimming, so a bird 'cuts the air' in his swift flight. Both species are provided in a similar way with tails and 'with the oarage of wings.' So the fish directs himself forward and advances to distant points by the aid of his wings [fins]. He uses his tail as a rudder in order to guide himself or change his route by a sudden movement from one area to another. Birds also exercise their wings in the air as if they were floating on water, using them in the way one would use one's arms. By use of their tails they are able to direct themselves upward or downward at will.

Book 5: The Fifth Day, chapter 14.47

There is one name for 'bird', but there are various species. Who can know them all or hold their names in memory? There are birds, for example, who live on flesh. Hence, they have sharp claws, a curved and sharp beak, and are swift on the wing. Thus they live by plunder, and are able to lay hold of what they pursue, and with their beaks and claws eviscerate it. There are birds, also, that search for and find their food in seeds. Others search for different kinds of food as they come upon them. There is diversity, too, in the way in which they group together. Those birds that are intent on plunder are devoid of this tendency. They do not act in common, because of their rapacity and the necessity of snaring their prey. Hence they disassociate themselves from groups for greed avoids participation moreover, a large flock would easily betray its own purposes. For birds of this sort there is no group life except that of conjugal relationship. This is the mode of life among the eagles and hawks. On the other hand, birds such as doves, cranes, starlings, crows, ravens, and even thrushes flock together for the most part.

Book 5: The Fifth Day, chapter 22.74-76

Now, having discussed just briefly the nature and beauty of flying creatures (we do not have time to describe every creature of the same or similar species), let us consider what diversity there is among birds themselves. We find that the crow has talons which are divided and separated, whereas nature has formed that part differently in the raven, even in her young. Those birds that feed on flesh have hooked talons, to enable them to seize their prey. Those that are accustomed to swimming have feet which are broad, with their parts bound and joined together by a kind of membrane. Here we find examples of admirable design in nature. In one case, flight or the acquisition of food is made easier. In the other, assistance is given in the art of swimming, whereby this act, too, is made easier. They use their feet as oars in ,such a manner that a current of water is propelled by the broad formation of the membrane attached to their feet. We can easily comprehend why a swan has a rather long neck. With a body that is somewhat corpulent, the swan cannot easily reach the lowest depths in search for food. Hence, the neck acts as a sort of advance scout for the rest of the body when on the lookout for food in the deep waters. This long neck has the additional advantage of giving a sweeter and more modulated tone to the swan's cry, which becomes clearer the .more frequently it is exercised. How sweet is the chant from the tiny throat of a cicada! In the heat of midsummer 'they rend the thickets' with their songs. The greater the heat at midday, the more musical become their songs, because the purer the air they breathe at that time, the clearer does the song resound. The bees, too, have a song that is not unpleasant. In that hoarse voice of theirs is an agreeable sweetness which we appear to have first imitated 'in the broken trumpet-blasts.' There is no sound more fitting than this to arouse hearts to vigorous action. Yet they have this curious gift, although they are said not to possess the function of breathing through lungs, but to breathe in the air as food. Hence they die immediately if oil is poured over them, because they are unable to take in that breath of air when their pores are closed. If one were straightway to pour vinegar over them, they quickly revive, since vinegar has the power of quickly opening those pores which had been sealed by the mass of oil.

Book 6: The Sixth Day, chapter 5.30

But let us return to the creation of different species and reflect on the reason why the Lord formed some beasts, such as lions, tigers, and bears, with shorter necks, whereas other animals, such as elephants and camels, were created with longer necks. Do we not find clear reason for this in the fact that animals which are carnivorous do not need long necks? They bend down their necks and jaws to the earth in the act of feeding. They use them for waylaying a deer or for dismembering an ox or a sheep. On the other hand, the camel, a taller animal, would be unable to feed on the smallest plants unless in the process of feeding he was able to extend his long neck to the ground. Accordingly, to the camel there has been allotted a neck that is longer in proportion to his stature. This is true, also, in the case of such herbivorous animals as the horse and the ox.

Book 6: The Sixth Day, chapter 6.36-37

Inasmuch as we propose to discuss the nature of man, it is fitting that, by way of preface, something be said that reflects credit on him. There appears to be no creature which has more physical strength or by its size inspires more terror than an elephant. No animals are as fierce as the lion and the tiger. Yet these beasts serve the interests of man and as the result of man's training lay aside their natural instincts. They forget their innate propensities and assume those which are imposed on them by command. Why need I say more? They are taught as if they were children. They cringe like weaklings and are lashed like timid creatures. They are corrected as are those subject to us and assume our habits since they have lost their own peculiar impulses. Wonderful, therefore, is the work of nature in both great and little things, for 'wonderful is the Lord on high.' Just as we admire the level plains no less than we do the high mountains, so we marvel no more at the height of the cedar than we do at the fruitfulness of the vine or of the modest olive tree. In like manner, I admire the elephant for his hugeness no less than the mouse for the fact that he inspires the same elephant with terror. Nature, therefore, has the power of causing fear in certain aspects and of being fearful in others. Each and every creature is endowed with certain characteristics which are their special mainstay. The elephant is a formidable object to a bull, but is fearful of a mouse. The lion, king of beasts, is disturbed by the slight sting of a scorpion and dies from the bite of poisonous serpent. The lion has extraordinary beauty as he shakes his mighty mane and raises his head on high. Yet, who does not marvel at the fact that huge bodies are subject to death from a scorpion's slight sting so slight as to be without substance?