part of gonadal sheath testis testis sheath This testis sheath consists of an outer epithelial layer of pigment cells and a thin, circumferential layer of muscle cells, separated from each other by a basal lamina. A second basal lamina separates the muscle layer from the testis lumen. It forms during the pupal stage both from cells of the testis and from cells of the genital disc (Kozopas et al., 1998). FBbt:00004955 fly_anatomy.ontology male-specific anatomical entity