Here the yolk of the rudimental egg, hitherto imperfectly formed, puts on its mature appearance of a thick yellow fluid; while the rudimental chick or embryo, lying on the surface opposite to that by which it had been attached to the ovarium, is white, and somewhat like paste. The white, or _albumen_, of the egg now becomes diffused around the yolk, being secreted from the blood vessels of the egg-pipe, or oviduct, in the form of a thin, glassy fluid; and it is prevented from mixing with the yolk and the embryo chicken by the thin membrane which surrounded them before they were detached from the egg-cluster, while it is strengthened by a second and stronger membrane, formed around the first, immediately after falling into the oviduct. This second membrane, enveloping the yolk of the germ of the chicken, is thickest at the two ends, having what may be termed bulgings, termed _chalazes_ by anatomists; these bulgings of the second membrane pass quite through the white at the ends, and being thus, as it were, embedded in the white, they keep the inclosed yolk and germ somewhat in a fixed position, preventing them from rolling about within the egg when it is moved. The white of the egg being thus formed, a third membrane, or, rather, a double membrane, much stronger than either of the first two, is formed around it, becoming attached to the chalazes of the second membrane, and tending still more to keep all the parts in their relative positions. During the progress of these several formations, the egg gradually advances about half way along the oviduct. It is still, however, destitute of the shell, which begins to be formed by a process similar to the formation of the shell of a snail, as soon as the outer layer of the third membrane has been completed. When the shell is fully formed, the egg continues to advance along the oviduct, till the hen goes to her nest and lays it. From ill health, or accidents, eggs are sometimes excluded from the oviducts before the shell has begun to be formed, and in this state they are popularly called _wind-eggs_. Reckoning, then, from the shell inward, there are _six_ different envelopes, of which one only could be detected before the descent of the egg into the oviduct: the shell; the external layer of the membrane lining the shell; the internal layer of same lining; the white, composed of a thinner liquid on the outside, and a thicker and more yellowish liquid on the inside; the bulgings, or chalaziferous membrane; and the proper membrane.