The image at top left is of a single cell. The egg we eat at breakfast—any bird's egg, really—is one cell. The yolk is a cytoplasmic mass of lipids, and the membrane around it is the plasma membrane. The rest of it: the chalazae, the "white" of the egg, the thin membranes lining the shell, and the shell itself, are all products of secretory activity, lying over the true cell.
Eggs like this are produced in the single ovary, in somewhat the same way mammalian eggs are. At the right above you see one of the "fingers" of the hen's ovary, and it contains a fair number of eggs (F) in various stages of development. The yellow part is what's developing here. Each of the round structures will become an egg yolk, on which, if and when fertilized, the embryo will feed during development.
Notice that there isn't anything resembling a zona pellucida, a membrana granulosa, or a cumulus oophorus here. There's just a bunch of follicles with yolky eggs in them. Eventually one will get large enough to be released, and when it does an opening will form on the surface; the follicle will split open, and the large egg will drop out into the upper end of the oviduct.Ovary, chicken; H&E stain, paraffin section, 20x
Close This Window