Electron microscope studies on the oocyte of the fresh‐water mussel (Anodonta), with special reference to the stalk and mechanism of yolk deposition

Abstract

An interesting relationship exists between the ovary and the developing oocyte in the fresh‐water mussel. As the oocytes grow, they elongate and bulge into the ovarian cavity. In the early stages, the nucleus migrates from the attached region (“foot”) to the distal region of the cell. With continued growth and maturation the connection between the proximal “foot” and distal nucleated portion becomes reduced to a narrow stalk. Microtubules appear in the young oocytes as they start to elongate and become packed in the stalks of older oocytes. It is suggested that the microtubules function as supporting structures and possibly also as channels for the transfer of materials from one portion of the oocyte to the other. The fine structure of the oocyte reveals evidence that the developing yolk bodies or spheres are formed, in part at least, by the incorporation of many smaller “precursor yolk vesicles.” These appear in the region of the Golgi complex and are presumed to be derived from the Golgi saccules. The oocyte contains an unusually well developed endoplasmic reticulum whose cisternae are filled with a rather conspicuous material.