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.

4. At the same period the viscera are visible, but the stomach, and intestines, and the veins from the heart still appear to extend towards the navel. From the navel a vein appears to extend upon the membrane which encloses the yolk, and the yolk itself is at this period fluid, and more abundant than in its natural state. The other extends to the membrane which encloses the whole membrane containing the embryo, and the membrane of the yolk and the fluid between them, and when the young birds have grown a little more, part of the yolk goes to one end, and part to the other, and between them is the fluid white; but the white is still below the lower part of the yolk, where it was at first, but at the tenth day the white disappears, for it has become small, viscid, thick, and rather yellow.

5. This is the position of all the parts: the first and last part adjoining the shell is the membrane of the egg, not the membrane of the shell, but beneath this. This contains the fluid white; within this is the young bird, and a membrane surrounding it, and separating it from the fluid; beneath the embryo is the yolk, to which one of the veins extends, and the other to the white which encloses it. A membrane containing a fluid resembling sanies encloses the whole, and then another membrane which surrounds the embryo itself, as I observed, and separates it from the fluid. Below this the yolk, enclosed in another membrane, which is reached by the umbilical cord from the heart, and the great vein, so that the embryo does not appear to be in either of the fluids.

6. About the twentieth day, if the hatching has been delayed beyond this period, the young bird is able to chirp when moved externally, and if the shell is taken off, by this time also it is downy. The head is placed over the right leg upon the side, and the wing is over the head. At this period the chorion-like membrane is visible, which is united with the lowest membrane of the shell, to which one of the umbilical cords passes, and the young bird is complete. The other chorion-like membrane is also visible, enclosing the yolk. To this the other umbilical cord extends. Both of these cords are attached to the heart and the great vein. At the same period the cord which is attached to one chorion falls off, and is separated from the animal, but the one which passes to the yolk remains suspended from the young bird by a thin bowel, and a considerable portion of the yolk is contained in the young bird, and some of it is found in the stomach.

7. At this period also they eject an excrementitious matter into the external chorion, and contain it in the stomach. The external excrement is white, the internal yellow. At last the yolk, which has been continually wasting and advancing, is entirely taken up and enclosed in the young bird. So that portions of it may be observed in the intestines of birds if they are dissected on the tenth day after exclusion from the egg. But it is set at liberty from the navel, nor does any communication remain, but the whole is separated. About the before-mentioned period the young bird sleeps, but it stirs itself, and looks up, and chirps when it is touched, and the heart swells up with the navel, as if the embryo were breathing. This is the manner of the development of the chick in the egg.

8. Birds also produce some barren eggs, as well as those from sexual intercourse, but they produce nothing after incubation. This is particularly observed in pigeons. Double eggs have two yolks; in some a thin division of white prevents the yolks from mixing together; others have not this division, but touch each other. There are some hens which always lay double eggs, and in these the peculiarities of the yolks have been observed; for a certain bird having laid eighteen eggs, hatched two chickens from each of them, except those that were addled; all the rest were productive, except that one of the twin chickens was large and the other small in each. The last, however, was monstrous.