Page:The Works of William Harvey (part 1 of 2).djvu/369

 ON GENERATION. 2G9

At the exclusion from the shell, consequently, certain death hangs over one or other, if not over both.

Fabricius either not observing the above words of Aristotle, or neglecting them, says : " If an egg have now and then two yelks, it engenders a chick having four legs or wings, and two heads a monster, in short; never two chicks distinct from one another, and that can be spoken of as a pair ; there is but one trunk, to which are appended two heads, &c."

Whence we may infer that he himself had never seen nor heard from credible persons that such eggs produce two pullets, and therefore that he agrees with me in regarding such eggs as rare, and in holding that they never produce two chicks both alike capable of living.

I am surprised nevertheless that, with the authority of Aris- totle before him, he should have said that " two chicks, distinct and separate, are never produced from such eggs," but always a monster; the rather as he thinks that the embryo is engen- dered from the chalazse as from the appropriate matter, and he could not but see that there are four chalazse in every twin- egg.

I should rather imagine that when two vitelli are included by the same albumen in a twin-egg, and are so intimately asso- ciated that their cicatriculse, when they are resolved together, con- stitute a single eye or colliquament, may engender a monstrous embryo with four feet, two heads, &c., because I see nothing to hinder this ; and such a production do I conceive to have been engendered by the egg of which Fabricius speaks.

But where two yelks have existed separately, parted by their several membranes, and furnished with chalaza?, albumens, and all else requisite to the generation of the chick, I hold that we must conclude, with Aristotle, that such an egg, as it has all the parts of two eggs except the shell, so does it also possess the faculty or faculties of as many; and unless it be a wind or barren egg, that it will for the most part produce two embryos, and but rarely a single monstrous individual.