| Abstract
| - The origin of yolk granules and the development of their internal structure are studied in a molluscan species. The yolk granules are revealed as a mass of vesicles transformed from the Golgi apparatus, which is termed here “grouped yolk vesicles (GYV).” Larger vesicles among them are multivesicular and also contain lamellar structures and dense particles, about 80 A in diameter. As the yolk vesicles in the GYV grow, the inner lamellar structures gradually increase and are concentrated. At the same time, yolk crystals in the yolk vesicles, consisting of the dense particles, increase in size. These dense particles also occur freely in the matrix and along the lamellar structures. They often show annular or basket-like structure and are continuous with fibrous structures in the matrix and the lamellar structures. These developed yolk vesicles or young yolk granules occur first in contact with smooth ER and are later surrounded by it.
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