[Structure of the follicular epithelium of the gonads Neva lamprey Lampetra fluviatilis (classification of the follicular epithelia of vertebrates)].

During its fluvial life, the ovarian follicular epithelium of Lampetra fluviatilis undergoes polarity formation--in the animal hemisphere the follicular epithelium is flattened, in the vegetative--it undergoes a secretory specialization: as the secrete is accumulating, the follicular cells increase in volume and height, acquiring a cubical form. In connection with monotonous or differentiating morpho-physiological alterations of follicular epithelium within a single follicle during the period of rapid oocytic growth, it is suggested to widen the idea on kinds of its secondary transformation in the vertebrates. It is suggested to differ: 1) common secondary transformation, when secondary flattening (for example, in birds) or secondary specialization (for example, in fish demersal roe) embraces the whole epithelium of the follicle. In case of common secretory specialization, it can be a) isomorphous--at identical convertion of the epithelium in the whole follicle (for example, in sheatfish), b) dimorphous--when there is a certain difference in the character and degree of secretory specialization of the follicular epithelium in various follicular areas (for example in Myxine glutinosa); 2) unipolar secondary transformation when the follicular epithelium undergoes secondary flattening or secretory specialization only in the area adjacent to one of the oocyte poles (for example, in Lametra fluviatilis and Blennis follis). Follicular epithelium of the lamprey testis, unlike in other Anamnia, does not form spermatocysts; implantation of spermatids and spermia into cytoplasm of the follicular cells is not observed. Thus, histological structure of Cyclostomata testis is at a lower stage of development than in other Anamnia.