The asexual stage is termed a "nematogen"; it produces "vermiform" (worm-like) larvae in the axial cell. These mature through direct development to form more nematogens. Nematogens proliferate in young cephalopods, filling the kidneys. Later, as the hosts mature, sexual forms called "rhombogens" are formed. They are hermaphrodites, with gonads of both sexes. The rhombogens self-fertilise, and later release larvae.