This solution therefore increases rapidly in quantity, particularly in its internal region, which, as it expands, forces out and obliterates the external regions. This change is effected in the course of a single day, as is shown in the second figure of Fabricius. It is very much as it is with the eyes of those animals which have a very ample pupil, and see better by night than by day, such as owls, cats, and others, whose pupils expand very much in the dusk and dark, and, on the contrary, contract excessively in a brilliant light: one of these animals being taken quickly from a light into a shady place, the pupil is seen to enlarge in such wise that the coloured ring, called the iris, is very much diminished in size, and indeed almost entirely disappears.
Parisanus, falling upon these regions, is grossly mistaken when he speaks of “a honey-coloured, a white, a gray, and another white circle;” and says that “the fœtus is formed from the white middle point” (which, indeed, appears in these regions), and that “this is the semen of the cock.” That he may exalt himself on a more notable subtlety he continues: “Before any redness is apparent in the body of the fœtus, two minute vesicles present themselves in it; in the beginning, however, neither of them is tinged with red;” one of these he would have us receive as the heart, the other as the liver. But in truth there is neither any vesicle present sooner than the redness of the blood is disclosed; nor does the embryo ever suddenly become red in the course of the first days of its existence; nor yet does any of these vesicles present us with a trace of the liver. Both of them belong, in fact, to the heart, prefiguring its ventricles and auricles, and palpitating, as we shall afterwards show, they respond reciprocally by their systoles and diastoles.
Aristotle[175] appears to have known this dissolved fluid, when he says: “A membrane, too, marked with sanguineous fibres, surrounds the white fluid at this time (the third day), arising from those orifices of the veins.” Now the philosopher can neither be supposed by the words “white fluid,” to refer to the albumen at large, because at this period the membrane of the white is not yet covered with veins; it is only the membrane of the dissolved fluid which appears with a few branches of veins distributed over it here and there. And because he says: “this membrane, too,” as if he understood another than those which he had spoken of as investing the albumen and the yelk before incubation, and designated this one as first arising after the third day, and from the orifices of the veins.