CYTOCHEMICAL AND ULTRASTRUCTURAL STUDIES OF OOGENESIS IN THE DYTISCIDAE

Abstract

SUMMARY Oogenesis of Dytiscidae is characterized by a remarkable phenomenon occurring in the germarium: each oogonium, after a series of normal mitoses, is transformed into a preoocyte characterized by a mass of extra- chromosomal chromatin called the Giardina mass or body or ring (GB), from the name of its Discoverer. The preoocyte undergoes four differential mitoses and the GB stays in only one cell, the oocyte, the other fifteen becoming nurse cells. The behaviour of this extrachromosomal formation is interesting but its significance is not completely clear, partly because it disintegrates and disappears during growth of the oocyte. Cytochemical study has shown that at its appearance the GB consists predominantly of DNA and at the time of its destruction there is an increasing synthesis of RNA. The results were obtained with a variety of cytochemical and autoradiographic techniques and have been confirmed by various Authors. The nurse cells grow too and their nuclei undergo numerous endomitoses. DNA sy...