| Abstract: | During the cortical reaction, Carcinus maenas eggs successively released a fine granular material and a massive amount of ring-shaped elements that subsequently formed most of the fertilization envelope. The ring-shaped elements came from egg cortical vesicles and, owing to their striking morphology, acted as naturally occurring markers in ultrathin sections, which permitted us to understand the pathway of their intracellular transport. In this respect it was established that the ring-shaped elements and their enclosing vesicles originated in the endoplasmic reticulum both in ripe oocytes and early fertilized eggs maintained under in vitro conditions. The intracellular transport pathway of the endoplasmic reticulum-derived vesicles seemed to bypass the Golgi apparatus. Accordingly, the ring-shaped elements appeared to be released by direct exocytosis from the endoplasmic reticulum system. Finally, a tentative scheme of oocytes functioning is suggested for crustacean decapods, based on the remarkable similarities between the structure and ER origin of the ring-shaped elements involved in the cortical reaction and the disc-shaped granules traditionally considered as endogenous yolk precursors. The scheme implies that the oocyte ER system might produce a precursor common to the cortical reaction exudate and to the endogenous yolk, in the form of the ring- or disc-shaped elements. |
