part of develops from male genital disc seminal vesicle fly_anatomy.ontology Enlarged distal region of the vas deferens. It connects the testis, via the testicular duct, to the main region of the vas deferens. The seminal vesicles taper into the twisted narrow portions of the vasa deferentia, which in turn opens into the anterior ejaculatory duct. FBbt:00004958 UBERON:0006868 vas deferens ventral ectoderm derivative male-specific anatomical entity multicellular structure