The ultrastructure of the macrogamete and young oocyst ofBarroussia schneideri inLithobius forficatus

Abstract

The ultrastructure of the macrogamete and young oocyst ofBarroussia schneideri was studied in the intestinal cells of naturally infected centipedes,Lithobius forficatus. The macrogamete which was bounded by a pellicle consisting of a single outer membrane and two interrupted inner membranes, developed within a parasitophorous vacuole devoid of intravacuolar folds and tubules. The limiting membrane of the young macrogamete possessed few micropores and was surrounded by a layer of amorphous material which remained until after oocyst wall formation. Initially, the macrogamete surface had many invaginations. These disappeared as the wall-forming bodies (WFB) which appeared to be of one type only, became located at the cell periphery. The cytoplasm of the mature macrogamete contained WFB, polysaccharide granules, electron-dense bodies, lipid globules, Golgi bodies, mitochondria, vesicles and abundant rough endoplasmic reticulum. At least one additional membrane was formed during oocyst wall formation and the material for the wall was deposited between the macrogamete cytoplasmic membrane and two external membranes. During oocyst wall formation,Barroussia schneideri seems unlike the Eimeriidae so far studied in that vacuoles lining the periphery of the cytoplasm remained after the WFB contents dispersed.