Almost all species are hermaphrodites, in other words they function as both males and females at the same time – except that in two species of the genus Ocryopsis individuals remain of the same single sex all their lives. The gonads are located in the parts of the internal canal network under the comb rows, and eggs and sperm are released via pores in the epidermis. Fertilization is external in most species, but platyctenids use internal fertilization and keep the eggs in brood chambers until they hatch. Self-fertilization has occasionally been seen in species of the genus Mnemiopsis, and it is thought that most of the hermaphroditic species are self-fertile.