"No less should we agree with Aristotle as to the sovereignty of the heart, in dealing with the following and similar questions: Does it receive motion and sensation from the brain, blood from the liver; or is it the origin of the veins and of the blood? For they who try to refute him leave out, or do not grasp, the main argument, which is that the heart is the first part to exist and has in it blood, life, sensation, motion, before the brain or the liver has been made or is clearly to be distinguished, or at least before either can perform any function. So the heart with its own proper organs constructed for motion--as it were, an internal animal--is the earlier formed; and, this being the first made part, it is the will of nature that thereafter the entire animal be made, nourished, preserved, perfected by the heart to be its achievement and abode. The heart is governor everywhere, like the chief in a commonwealth with whom is lodged the first and highest authority. In an animal all power is derived from and depends upon the heart as its origin and foundation."[122] The main argument, which is that the heart is the first part to exist, is simply the argument from the development of the embryo in the hen's egg. The study of this development day by day had been recommended by one of the Hippocratic writers,[123] and Aristotle had laid stress upon the changes in the embryo during incubation.[124] Harvey, in his turn, had studied them carefully. The ancients could have made their observations only with the naked eye, but Harvey had the aid of a simple lens, though of nothing approaching in power to a microscope.[125] In the treatise of 1628 he speaks as follows of what he thus observed:-- "If you turn to the formation of the chick in the egg, the first thing to exist therein, as I have said, is a mere vesicle, or auricle, or pulsating drop of blood. Afterward, when growth has gone on, the heart is completed.... In a hen's egg after four or five days of incubation I have shown the visible presence of the rudiment of the chick in the form of a little cloud; in an egg, that is, which had been immersed in clear tepid water after removal of the shell. In the middle of the aforesaid little cloud there was a palpitating bloody point, so fine that in contracting it disappeared and became invisible, but reappeared on its relaxation, looking like the point of a needle, and of a ruddy color; so that being now visible and now invisible, as though now existent and now non-existent, it evinced palpitation and the beginning of life."[126] In the same treatise Harvey promises to publish more observations