Histomorphology of the ovaries of the earthworm, Dendrobaena atheca Cernosvitov (Annelida, Clitellata: Oligochaeta)

Abstract

This comprehensive study was undertaken to reveal the ovarian histomorphology in the oligochaetous clitellte, Dendrobaena atheca Cernosvitov. Efforts were, in fact, made to obtain proper histological preparations. So, various types of thin serial sections of ovaries were carefully obtained, stained and examined. Two small ovaries, at the beginning of breeding seasons, were seen in segment thirteen. Subsequently, they extremely increased in size and became fully formed. They demonstrated six principal cell types: peritoneal cell, follicular cell, stromal cell, oogonium, oocyte and trophocyte (nurse cell). The first three cell types were somatic, whereas the other three were germ and germ-line. All cell types were, as much as possible, properly described. Dividing oogonia were seen to produce oocytes and trophocytes simultaneously. The produced cells were seen to be interconnected. The stromal cell, a newly described cell type, exhibited several specific cell characteristics. Ovaries showed no internal lumens. The small ovaries showed only two distinct histological zones, whereas the large ones showed three such zones. Germ and germ-line cells showed an obvious arrangement in ovarian zones. Accordingly, the chief conclusions are: (1) ovaries are nutrimental due to presence of trophocytes (2) ovaries are solid and not sac-like organs due the lack of internal cavity (3) stromal cell can be considered a new cell type as it demonstrates several specific cell features (4) Ovarian zonation is caused by production and arrangement of germ and germ-line cells (5) intercellular connections are due to incomplete cell divisions.

Keywords

solid nutrimental ovaries - trophocytes - oocytes - follicular cells - stromal cells