Fine structure of the ovary of Schizomus palaciosi (Arachnida: Schizomida)

Abstract

The ovary of Schizomus palaciosi is an unpaired structure located in the medioventral opisthosoma. It consists of a flat tube with compressed lumen. The wall of the ovarian tube is composed of a monolayer of epithelial cells and muscle cells. Early oocytes are embedded in the dorsal wall of the ovarian tube. Here the first growing phase starts increasing the amount of cytoplasm and the size of the nucleus. This increase results in an outward movement (externalization) of the oocyte, i.e., the oocyte grows into a pouch made of the basal lamina of the epithelium and is finally almost completely exposed towards the hemolymphatic space or adjacent tissues. A funicle made of epithelial cells connects the oocyte with the ovarian tube. Now, solitary vitellogenesis starts and the oocyte becomes much larger (second growth phase) depositing a complex protein yolk and lipid yolk in the cell body. In the outward stages, the funicle cells facing the oocyte secrete material that is deliverd into the space between funicle and oocyte. Thus it is added to the simple basal lamina of the ovarian epithelium which first formed the pouch alone. The pouch thus consists finally of two more or less distinct layers. A vitelline envelope which is deposited between pouch and oocyte in most Chelicerata as a primary egg shell parallel to vitellogenesis was not observed. Fine structure of the cell types involved are dealt with for the first time for a schizomid species. Results are discussed under comparative and functional aspects.