Formation and function of accessory nuclei in the oocytes of the bird louse, Eomenacanthus stramineus (Insecta, Mallophaga). I. Ultrastructural and histochemical studies.

In the oocytes of Eomenacanthus stramineus accessory nuclei arise by budding from the nuclear envelope. It is suggested that microtubules and the thick layer of the nuclear lamina are involved in this process. Newly formed accessory nuclei contain aggregations of fibrillogranular material. These aggregations are slightly Feulgen positive, RNA negative and stain positively with the Ag-NOR method. During later developmental stages one dense, RNA-positive inclusion appears in each accessory nucleus. These inclusions consist of an Ag-NOR-positive cortical layer and an Ag-NOR-negative core. The function of accessory nuclei in the species investigated is discussed in the light of these results.