[Morphodynamics of follicular epithelium during elasmobranch oogenesis (the problem of histologic paralellisms and convergences in the development of vertebrate follicular epithelia)].

Morphodynamics of follicular epithelium in oogenesis of 3 species of sharks and one species of skates studied is characterized by transformation of follicular flattened unilayered epithelium into columnar unilayered and false pseudostratified epithelium which subsequently undergoes secondary flattening and loses its false pseudostratification. In skates, during the process described above, the follicular epithelium becomes anisomorphous at the expense of differentiation of some follicular cells into large ones with two bipolar processes. Developmental and structural similarity of false pseudostratified follicular epithelia in sharks and birds, as well as similarity of anisomorphous follicular epithelia in skates and Squamata are considered as a certain demonstration of histological parallelism in the development of follicular epithelia of Vertebrata. On the other hand, large cells of anisomorphous follicular epithelia in skates and Squamata and trophocytes of polytrophic ovarioles in insects, in their relation to oocyte, are considered as analogous structures giving an example of histological convergency.