Chapter II.

1. The eggs of all birds are alike and have a hard shell, if they are produced by sexual intercourse and are not decayed, for domestic fowls sometimes lay soft eggs. Birds' eggs are two-coloured, externally white, internally yellow. The eggs of birds inhabiting the sides of streams and lakes differ from those living on dry land, for in the eggs of aquatic birds the yolk bears a much larger proportion to the white.

2. The colours of eggs vary in different kinds of birds. Some have white eggs, as pigeons, partridges; some yellow, as those inhabiting streams; others are spotted, as those of the meleagris[194] and phasianus;[195] the eggs of the cenchris are red like vermilion. In the egg itself there is a difference; for one end is pointed, the other round. The round end is produced first. The large, sharp eggs are males; those which are round and circular at the sharp end are females.

3. They are matured by incubation. Some are hatched spontaneously in the earth, as in Egypt, being buried in dung; and they say that in Syracuse a drunkard placed eggs beneath his mat, and drank without ceasing until the eggs were hatched; and eggs placed in warm vessels have been matured and hatched spontaneously.

4. The seminal fluid of all birds is white, like that of other animals; and when they copulate the female receives the male semen near the diaphragm. The egg at first appears small and white, afterwards red and bloody; as it grows it becomes quite ochreous and yellow; when it becomes larger a distinction is made, and the internal part becomes yellow, the external white; and when it is perfected it is set at liberty, and excluded just at the period when it is changing from soft to hard. So that during exclusion it is not hardened; but as soon as it is excluded it thickens and becomes hard, unless it is diseased. And eggs have been known to be excluded in the state in which all eggs are at a certain period of their growth; for they were entirely yellow, as the young bird is afterwards. Such have also been observed in the domestic fowl beneath the diaphragm, where the eggs of the hen are placed, entirely yellow, and as large as eggs usually are. This has been considered ominous.

5. They are mistaken who say that the hypenemia (barren eggs) are the remains of former acts of sexual intercourse; for young birds, as fowls and geese, have been frequently observed to lay such eggs without any sexual intercourse. Barren eggs are smaller, not so sweet, and more fluid than fertile eggs, and they are more numerous. If they are placed under a bird, the fluid part never thickens, but both the yolk and the white remain in their original state. Many birds produce these eggs, as the domestic fowl, partridge, pigeon, peafowl, goose, and chenalopex.[196]

6. Eggs are hatched more readily in summer than in winter; for in the summer the domestic fowl will hatch in eighteen days, but in winter sometimes in not less than twenty-five days. Some birds also are more adapted for incubation than others. A thunder-storm during the season of incubation will destroy the eggs. What are called cynosura and uria (addled eggs) are more frequently produced in the summer. The hypenemia[197] are by some persons called zephyria, because they say that birds receive these winds in the spring. They do the same thing if they are touched with the hand. The hypenemia become fertile; and eggs that are produced by sexual intercourse are changed to another kind, if the hen which contains either hypenemia or fertile eggs has sexual intercourse with another bird before the eggs begin to change from yellow to white, and the hypenemia become fertile, and the fertile eggs produce birds of the nature of the second male.

7. But if the change from yellow to white has already taken place, neither the barren nor the fertile eggs are altered, so as to change to the nature of the second male. And if the sexual intercourse should be discontinued while the eggs are small, those which existed previously undergo no change, but if the act is repeated, a rapid increase in size takes place. The nature of the white and yolk of the egg is different, not only in colour, but in other properties, for the yolk coagulates with cold, while the white remains fluid, but the white coagulates with heat, which the yolk does not, but remains soft, if it is not burnt; and it becomes consistent and dry by boiling rather than roasting.

8. The white and yolk are separated from each other by a membrane. The chalazæ at the extremities of the yolk have nothing to do with generation, as some persons suppose. These spots are two, one below and one above. If many whites and yolks of eggs are taken out, and mixed together in a vessel, and cooked with a slow and moderate heat, the yolks will all collect in the middle, and the whites will surround them. Young domestic fowls begin to lay eggs at the beginning of the spring; they lay more than those which are older, but those of the young birds are smaller, and if birds are not permitted to incubate, they are destroyed and become sick.

9. After copulation birds ruffle and shake themselves, and often cover themselves with chaff, and this also they do when they have laid. Pigeons draw up their tail, geese go and bathe. The pregnancy and conception of barren eggs is quick in most birds, as in the partridge, on account of the violence of their sexual desires; for if the hen stands in the way of the breath of the male, she conceives, and immediately becomes of no use for fowling; for the partridge appears to have a very distinct smell. The production of the egg after copulation, and the production of the young by incubation, do not occupy the same length of time in all birds, but varies according to their size. The egg of the domestic fowl is perfected in ten days after sexual intercourse, and that of the pigeon in a shorter time. Pigeons are able to retain their eggs even in the act of parturition. If they are disturbed by anything occurring in the neighbourhood of their nest, or a feather be plucked out, or if anything else troubles or disturbs them, they retain the egg they were about to lay.

10. This is peculiar to pigeons, and so is the following: for they kiss each other when the male is about to mount, or else they will not endure it. The older bird first gives a kiss, but afterwards he mounts without kissing, but younger birds always kiss before copulation. This also is peculiar to these birds. The females kiss and mount upon each other like the males, when there is no male present. They do not project anything into each other, but produce more eggs than those which produce fertile ones; from these eggs nothing is hatched, but they are all barren.