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] [196] Œnas tadorna. 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. [197] Eggs formed without sexual intercourse.