Note b — BOOK VII.

As the Shell and Skin keep the Yolk and two Whites together; so each of the Parts, (the Yolk and inner White at least,) are separated by Membranes, involving them. At each End of the Egg is a Treddle, so call’d, because it was formerly thought to be the Sperm of the Cock. But the Use of these, (saith Dr. Harvey in Willugh. Ornith. c. 3.) is to be as ’twere, the Poles of this Microcosm, and the Connections of all the Membranes twisted and knit together, by which the Liquors are not only conserv’d, each in its Place, but do also retain their due Position one to another. This, although in a great Measure true, yet doth not come up to what I have my self observ’d; for I find, that these Chalazæ, or Treddles, serve not barely to keep the Liquors in their Place, and Position to one another; but also to keep one and the same Part of the Yolk uppermost, let the Egg be turn’d nearly which way it will; which is done by this Mechanism: The Chalazæ are specifically lighter than the Whites, in which they swim; and being brac’d to the Membrane of the Yolk, not exactly in the Axis of the Yolk, but somewhat out of it; causeth one Side of the Yolk to be heavier than the other; so that the Yolk being by the Chalazæ made buoyant, and kept swimming in the Midst of two Whites, is by its own heavy Side kept with the same Side always uppermost; which uppermost Side I have some Reason to think, is that on which the Cicatricula lies; that being commonly uppermost in the Shell, especially in some Species of Eggs more I think than others.