Ovarian oocytes of the fresh-water Triclads Dugesia lugubris and D. benazzii have been studied by means of histochemical and electron microscopical techniques. In the oogenesis, two periods have been distinguished which may be characterized as previtellogenetic and vitellogenetic. During the first period oocytes slightly increase in size and their cytoplasm shows a high RNA content. At the onset of vitellogenesis many small vesicles filled with electron dense granules of 270-280 Å begin to appear; later on these vesicles fuse together and form large yolk globules. The oocytes remarkably increase in size throughout this period and their stainability shows clear changes. On the basis of reported findings the egg of these Dugesia species can be regarded as slightly lecithal.
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Con il contributo del Ministero per i Beni e le Attività Culturali