Maturing females of the octopod Japetella diaphana (Hoyle) develop a luminous oral ring. Studies of specimens of different size show that this structure develops from a muscular ring which undergoes great cellular proliferation, associated with gradual degeneration of the original muscle. The light-producing cells (photocytes) have a relatively uniform cytoplasm whose most characteristic components are small mitochondria, granular aggregates and microtubular or microfibrillar bundles. It is concluded that the original muscle tissue is not transformed directly into luminous tissue.
Possible uses of the luminescence are discussed, based on the postures adopted by live specimens in shipboard aquaria.