After six hours incubation the cicatrice is considerably dilated, and the ball formed by the amnios is easily discovered; this ball is filled with a liquor, in the middle of which the head of the chicken and back-bone are distinctly seen. In about six hours more the little animal is seen more distinctly; in another six hours the head is grown larger, and the spine lengthened; and at the end of twenty-four hours the neck begins to lengthen, the vertebræ of the back appears of a white colour, and the head to turn to one side. The vertebræ are disposed on each side of the spine, like small globules; and almost at the same time the small wings begin to shoot, and the head, neck, and breast are lengthened. After thirty hours nothing new appears, but every part of the little animal is considerably increased, especially the _amnios_. Around this membrane the umbilical vessels are seen of a darkish colour. At the end of thirty-eight hours, the chicken being grown much larger, its head is large, and in which are distinguished three vessels surrounded with membranes, which also cover the back bone, through which the vertebræ are still seen. In forty hours, continues Malpighius, it was wonderful to see the chicken alive, floating in the liquor; the back bone was increased, the head was turned on one side, the vesicles of the brain were less apparent, the first outlines of the eyes appeared, the heart beat, and the circulation of the blood was begun. Malpighius then gives the description of the vessels and course of the blood, and reasonably supposes that, though the heart does not beat before thirty-eight or forty hours incubation, it still existed before that time, like the other parts of the chicken; but on examining the heart in a dark room, he discovered not the least glimpse of light to proceed from it, as Harvey insinuates. At the end of two days the chicken is seen floating in the liquor of the amnios; in which the head, composed of vesicles, is turned on one side; the back bone and vertebræ are lengthened; the heart, which then hung out of the breast, beat three times; for the fluid it contains is impelled into the ventricles of the heart, from thence into the arteries, and afterwards into the umbilical vessels. He remarks, that having separated the chick from the white of the egg, the motion of the heart still continued for a whole day. After two days and fourteen hours, or sixty-two hours of incubation, the chicken, although grown stronger, remained with its head bent downwards in the liquor, contained by the amnios; the veins and arteries were seen among the vessels of the brain; the lineaments of the eyes, and the spinal marrow, also appear extending the length of the vertebræ.