[Ultrastructural study of the normal development of the oocytes and of the follicle cells in Locusta migratoria (L.) (Orthoptera) (author's transl)].

Vitellogenesis in Locusta migratoria is studied by electron microscopy, and may be divided into two major periods: a. the first stage of growth (oocyte length from 0,8 mm to 1,8 mm) is characterized by protein synthesis and storage in the rER, by transfer of material of nucleolar origin into the oocyte perinuclear cytoplasm as well as by pinocytotic activity giving rise to granulo-membranous structures. At this stage the apical part of the follicle cells differenciates as attested by mitochondrial accumulation and microvilli development; b. the second period of vitellogenesis (oocyte length from 1,8 to 6,8 mm) is characterized by accumulation of hemolymphatic material which partly separates the follicle cells and progressively detaches the follicular epithelium from the oocyte. The intense uptake of this material by oocyte leads to the formation of typical yolk globules. The material of nucleolus origin disappears from the cytoplasm at the beginning of this stage. The secretory activity of the follicular epithelium starts by the end of this second period (oocyte length 4 mm), leading vitelline membrane formation, and intensifies when the chorion is formed. The secretory material is excreted in soluble form. In the vicinity of the oocyte, this material is submitted to a series of complex modifications: it precipitates again in granular form, progressively unites and finally leads to the "scale-like" structures which are characteristic of the chorion.