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. CHAPTER III. 1. The production of the bird from the egg is alike in them all, but the period of completion varies, as I observed before. In domestic fowls the first sign of alteration takes place after three days and nights. This period is longer in larger birds, and shorter in small birds. During this period the upper part of the yolk advances to the small extremity of the egg, which is the beginning of the egg. This is the part from which the chicken is excluded, and the heart is visible like a red spot in the white of the egg. 2. This spot palpitates and moves as though it were endued with life. From this, as it increases, two involved sanguineous passages like veins lead to each of the surrounding tunics; and a membrane which has sanguineous passages encloses the white at this period, and separates it from the venous passages. A short time afterwards the body is distinguished, at first very small and white, but the head is distinct, and in this the eyes are the most enlarged. And this continues for some time, for afterwards the eyes are reduced in size and approach each other, but the lower part of the body has not at first any proportion to the upper part. 3. One of the passages from the heart extends into a circle around the embryo, and the other to the yolk, as if it were an umbilical cord. The origin of the young bird is in the white, its nutriment is derived from the yolk through the umbilical cord. On the tenth day, the whole of the young bird and all its parts are distinct, but its head is still larger than the rest of the body, and the eyes are larger than the rest of the head. They have no sense of sight. If the eyes are taken out at this period, they are larger than beans, and black; when the skin is taken from them, they are seen to contain a white and cold fluid, very brilliant in appearance, but without any hard substance. This is the manner of the development of the eyes and head.