Some eggs are white, as those of the pigeon and partridge, for instance; others are of a pale colour, as in the aquatic birds: others, again, are dotted all over with spots, as is the case with those of the meleagris; others are red, like those of the pheasant and the cenchris. In the inside, the eggs of all birds are of two colours; those of the aquatic kind have more of the yellow than the white, and the yellow is of a paler tint than in those of other birds. Among fish, the eggs are of the same colour throughout, there being, in fact, no white. The eggs of birds are of a brittle nature, in consequence of the natural heat of the animal, while those of serpents are supple, in consequence of their coldness, and those of fish soft, from their natural humidity. Again, the eggs of aquatic birds are round, while those of most other kinds are elongated, and taper to a point. Eggs are laid with the round end foremost, and at the moment that they are laid the shell is soft, but it immediately grows hard, as each portion becomes exposed to the air. Horatius Flaccus[1] expresses it as his opinion that those eggs which are of an oblong shape are of the most agreeable flavour. The rounder eggs are those which produce[2] the female, the others the male. The umbilical[3] cord is in the upper part of the egg, like a drop floating on the surface in the shell.

(53.) There are some birds that couple at all seasons of the year, barn-door fowls, for instance; they lay, too, at all times, with the exception of two months at mid-winter. Pullets lay more eggs than the older hens, but then they are smaller. In the same brood those chickens are the smallest that are hatched the first and the last. These animals, indeed, are so prolific, that some of them will lay as many as sixty eggs, some daily, some twice a day, and some in such vast numbers that they have been known to die from exhaustion. Those known as the "Adrianæ,"[4] are the most esteemed. Pigeons sit ten times a year, and some of them eleven, and in Egypt during the month of the winter solstice even. Swallows, blackbirds, ring-doves, and turtle-doves sit twice a year, most other birds only once. Thrushes make their nests of mud, in the tops of trees, almost touching one another, and lay during the time of their retirement. The egg comes to maturity in the ovary ten days after treading; but if the hen or pigeon is tormented by pulling out the feathers, or by the infliction of any injury of a similar nature, the maturing of the egg is retarded.

In the middle of the yolk of every egg there is what appears to be a little drop[5] of blood; this is supposed to be the heart of the chicken, it being the general belief that that part is formed the first in every animal: at all events, while in the egg this speck is seen to throb and palpitate. The body of the animal itself is formed from the white fluid[6] in the egg; while the yellow part constitutes its food. The head in every kind, while in the shell, is larger than the rest of the body; the eyes, too, are closed, and are larger than the other parts of the head. As the chicken grows, the white gradually passes to the middle of the egg, while the yellow is spread around it. On the twentieth day, if the egg is shaken, the voice of the now living animal can be heard in the shell. From this time it gradually becomes clothed with feathers; and its position is such that it has the head above the right foot, and the right wing above the head: the yolk in the meantime gradually disappears. All birds are born with the feet first, while with every other animal the contrary is the case. Some hens lay all their eggs with two yolks, and sometimes hatch twin chickens from the same egg, one being larger than the other, according to Cornelius Celsus: other writers, however, deny[7] the possibility of twin chickens being hatched. It is a rule never to give a brood hen more than twenty-five[8] eggs to sit upon at once. Hens begin to lay immediately after the winter solstice. The best broods are those which are hatched before the vernal equinox: chickens that are hatched after the summer solstice, never attain their full growth, and the more so, the later they are produced.