On the second day of the incubation, after the egg has been exposed to warmth for twenty-four hours, under the hen, as the cavity in the blunt end has enlarged greatly and descended, so has the internal constitution of the egg also begun to be changed. The yelk, which had hitherto lain in the middle of the albumen, rises towards the blunt end, and its middle, where the cicatricula is situated, is lifted up and applied to the membrane that bounds the empty space, so that the yelk now appears to be connected with the cavity by means of the cicatricula; and in the same measure as the yelk rises does the thicker portion of the albumen sink into the sharp or lower end of the egg. Whence it appears, as Fabricius rightly remarks, that Aristotle[173] was either in error, or that there is a mistake in the codex, when it is said, “In this time” (viz., between three and four days, and as many nights,) “the yelk is brought to the summit, where the commencement of the egg is, and the egg is exposed in this part,” i. e. under the enlarged empty space. Now Aristotle[174] calls the principium ovi, or commencement of the egg, its smaller end, which is last extruded. But it is certain that the yelk ascends towards the blunt end of the egg, and that the cavity there enlarges. And Aldrovandus is undoubtedly in error when he speaks as if he had experience of the fact, and says that the yelk rises to the sharp end. I will confess, nevertheless, that on the second or third day I have occasionally observed the cicatricula expanded and the beginning of the chick already laid, the yelk not having yet risen; this, however, happens rarely, and I am inclined to ascribe it to some weakness in the egg. On the second day of the incubation, or first day of inspection, the cicatricula in question is found to have enlarged to the dimensions of a pea or lentil, and is divided into circles, such as might be drawn with a pair of compasses, having an extremely minute point for their centre. It is very probable that Aldrovandus observed this spot, for he says: “In the midst of the yellow a certain whitish something makes its appearance, which was not noticed by Aristotle;” and also by Coiter, when he expresses himself thus: “On the second day there is in the middle of the yelk a part whiter than the rest;” Parisanus, too, may have seen it; he observes: “In the course of the second day I observe a white body of the size and form of a middling lentil; and this is the semen of the cock covered over with a white and most delicate tunic, which underlies the two common membranes of the entire egg, but overlies the tunica propria of the yelk.” I believe, however, that no one has yet said that this cicatricula occurs in every egg, or has acknowledged it to be the origin of the chick.