The Works of William Harvey M.D. / Translated from the Latin with a life of the author

by William Harvey

EXERCISE THE FOURTEENTH.

Of the production of the chick from the egg of the hen.

Of the growth and generation of the hen’s egg enough has already been said; and we have now to lay before the reader our observations on the procreation of the chick from the egg,—a duty which is equally difficult, and profitable, and pleasant. For in general the first processes of nature lie hid, as it were, in the depths of night, and by reason of their subtlety escape the keenest reason no less than the most piercing eye.

Nor in truth is it a much less arduous business to investigate the intimate mysteries and obscure beginnings of generation than to seek to discover the frame of the world at large, and the manner of its creation. The eternity of things is connected with the reciprocal interchange of generation and decay; and as the sun, now in the east and then in the west, completes the measure of time by his ceaseless revolutions, so are the fleeting things of mortal existence made eternal through incessant change, and kinds and species are perpetuated though individuals die.

The writers who have treated of this subject have almost all taken different paths; but having their minds preoccupied, they have hitherto gone to work to frame conclusions in consonance with the particular views they had adopted.

Aristotle,[170] among the ancients, and Hieron. Fabricius of Aquapendente, among the moderns, have written with so much accuracy on the generation and formation of the chick from the egg that little seems left for others to do. Ulyssus Aldrovandus,[171] nevertheless, described the formation of the chick in ovo; but he appears rather to have gone by the guidance of Aristotle than to have relied on his own experience. For Volcherus Coiter, living at this time in Bologna, and encouraged, as he tells us, by Aldrovandus, his master, opened incubated eggs every day, and illustrated many points besides those noted by Aldrovandus;[172] these discoveries, however, could scarcely have remained unknown to Aldrovandus. Æmilius Parisanus, a Venetian physician, having discarded the opinions of others, has also given a new account of the formation of the chick from the egg.

But since our observations lead us to conclude that many things of great consequence are very different from what they have hitherto been held to be, I shall myself give an account of what goes on in the egg from day to day, and what parts are there transmuted, directing my attention to the first days especially, when all is most obscure and confused, and difficult of observation, and in reference to which writers have more particularly drawn the sword against one another in defence of their several discordant observations, which, in sooth, they accommodate rather to their preconceived opinions respecting the material and efficient cause of animal generation than to simple truth.

What Aristotle says on the subject of the reproduction of the chick in ovo is perfectly correct. Nevertheless, as if he had not himself seen the things he describes, but received them at second hand from another expert observer, he does not give the periods rightly; and then he is grievously mistaken in respect of the place in which the first rudiments of the egg are fashioned, stating this to be the sharp end, for which he is fairly challenged by Fabricius. Neither does he appear to have observed the commencement of the chick in the egg; nor could he have found the things which he says are necessary to all generation in the place which he assigns them. He will, for instance, have it that the white is the constituent matter (since nothing naturally can by possibility be produced from nothing.) And he did not sufficiently understand how the efficient cause (the seminal fluid of the cock,) acted without contact; nor how the egg could, of its own accord, without any inherent generative matter of the male, produce a chick.

Aldrovandus, adopting an error akin to that of Aristotle, says besides, that the yelk rises during the first days of the incubation into the sharp end of the egg, a proposition which no eyes but those of the blind would assent to; he thinks also that the chalazæ are the semen of the cock, and that the chick arises from them, though it is nourished both by the yelk and the white. In this he is obviously in opposition to Aristotle, who held that the chalazæ contributed nothing to the reproductive powers of the egg.

Volcherus Coiter is, on the whole, much more correct; and his statements are far more consonant with what the eye perceives. But his tale of the three globules is a fable. Neither did he rightly perceive the true commencement of the chick in ovo.

Hieronymus Fabricius contends that the chalazæ are not the sperma of the cock; but then he will have it that “from these, fecundated by the seminal fluid of the cock, as from the appropriate matter, the chick is incorporated.” Fabricius observed the point of origin of the chick, the spot or cicatricula, namely, which presents itself upon the tunica propria of the yelk; but he regarded it as a cicatrice or scar left on the place where the peduncle had been attached; he viewed it as a blemish in the egg, not as any important part.

Parisanus completely refutes Fabricius’s ideas of the chalazæ; but he himself obviously raves when he speaks of certain circles, and principal parts of the fœtus, viz., the liver and heart. He appears to have observed the commencement of the fœtus in ovo; but what it was he obviously did not know, when he says, “that the white point in the middle of the circles is the semen of the cock, from which the chick is produced.”

Thus it comes to pass that every one, in adducing reasons for the formation of the chick in ovo, in accordance with preconceived opinions, has wandered from the truth. Some will have it that the semen or the blood is the matter whence the chick is engendered; others, that the semen is the agent or efficient cause of its formation. Yet to him who dispassionately views the question is it quite certain that there is no prepared matter present, nor any menstruous blood to be coagulated at the time of intercourse by the semen masculinum, as Aristotle will have it; neither does the chick originate in the egg from the seed of the male, nor from that of the female, nor from the two commingled.