[Relations between the evolution of the nucleolus and the brain hormone activity during oogenesis inNereis diversicolor O.F. Müller (Annelida, Polychaeta) under natural and experimental conditions].

Each stage of oogenesis: previtellogenesis, proteic yolk elaboration, carbohydrates synthesis, maturity, take place under a given hormonal rate. During the previtellogenesis and protein yolk elaboration stages (high hormonal rate), nucleolus is composed of three concentric zones: a fibrillar center, a fibrillar intermediate belt and a granular cortex. During the carbohydrates synthesis stage, which occurs after a rapid decrease of the hormonal rate, a new nucleolar organization appears. Nucleolus is then composed of fibrillar places scattered among a fibrillo-granular component. During the maturity stage (very low hormonal rate), the nucleolar material segregates into two hemispheres, then breaks up.The result of removal of cerebral activity was considered. In oocytes undergoing protein yolk elaboration, the absence of hormone rapidly produces the development of a large nucleolar vacuole. Then, vacuole decreases and nucleolus shows again a compact shape. The end of the experimental evolution is marked by the segregation of the nucleolar fibrillar and fibrillogranular components.Chronological study of the modifications occuring at the different cellular regions shows that the consequences of removal of hormonal activity are seen at the nucleolar level in advance of being detectable in cytoplasm. These results are discussed accordingly present notions about hormonal regulation of RNA synthesis.