Differentiation and ultrastructure of the spermatogonial cyst cells in the milkweed bug,Oncopeltus fasciatus

Summary The testes of the newly hatched larva of Oncopeltus fasciatus consist of three different cell types enclosed by the tunica propria: the germline stem cells, the apical cells, and the follicle border cells which are the predecessors of the cyst progenitor cells. There are usually twelve somatically derived apical cells per follicle that no longer divide during postembryonic development. Their fine structural organization remains constant from hatching until death from old age. The apical complex cells are surrounded by at least four germline stem cells which all send cell projections toward the apical complex cells. A testicular follicle includes at least four border cells at the fir…