Fine structure, development and cytochemistry of the spherulosome of Haplosporidium lusitanicum (Haplosporida).

Morphogenesis of the "spherulosome" (formerly termed the "spherule") of Haplosporidium lusitanicum is described. In the apical zone of the immature spore a very complex and irregular membranous system is formed. This membrane synthesis begins in a precise zone which we call the "membranous organizer region". Half way their maturation of the spore, this membranous system gradually becomes a well-organized vesicular system partially surrounded by a limiting membrane, thus forming the spherulosome. The organelle always occupies the apical region of the spore near the operculum. Toward the end of spore maturation the whole endosporoplasm becomes very dense and the spherulosome is difficult to observe. Cytochemical analysis by Thiéry's method revealed that the spherulosome membranes as well as the dense vesicle-like droplets acquire a dark deposit characteristic of glycoproteins.