[The establishment of polarity and bilateral symmetry in the oocytes of Gryllus domesticus L.].

1. The origin of polarity and bilateral symmetry of oocytes inGryllus domesticus L. has been studied. 2. The histology of the ovary and the process of oogenesis are described. 3. The germinal vesicle shifts into the posterior half of the oocyte, when these cells are 60 to 100 μm in length, thus indicating for the first time oocytic anteroposterior polarity. 4. Bilateral symmetry first appears, when the follicle reaches a length of 450 to 550 μm. This change from radial to bilateral symmetry is the result of the germinal vesicle leaving its position in the long axis of the cell and moving perpendicularly to this axis towards the follicular epithelium. 5. In follicles 60 to 100 μm in length the nucleolus comes to lie, under the influence of gravity, in the geopetal quarter of the germinal vesicle, and remains there. 6. No correlation can be found between geopetal position of the nucleolus and bilateral symmetry of the oocyte. 7. Oogenesis and the establishment of axes in the oocytes are not affected by centrifuging adults and last instars. 8. When the oocyte nucleus touches the follicular epithelium, changes occur in the structure and function of some epithelial cells. Those close to the germinal vesicle, with flattened nuclei, show reduced yolk secretion. Those at the opposite side show enhanced secretory activity. Presumably as a result of this differential secretory activity the shape of the oocyte becomes curved. 9. Only intact vitellogenetic oocytes show a banana-like form. 10. The ultrastructural examination of the previtellogenetic follicle indicates no predisposition for the direction of displacement of the oocyte nucleus, and therefore no predisposition of the plane of bilateral symmetry. 11. The hypothesis is discussed that the germinal vesicle itself initiates and directs the appearance of bilateral symmetry in the oocyte.