The ovary of teleosts is also often hollow, but in this case, the eggs are shed into the cavity, which opens into the oviduct .  Certain nematodes of the genus Philometra are parasitic in the ovary of marine fishes and can be spectacular, with females as long as 40 cm, coiled in the ovary of a fish half this length.  Although most normal female vertebrates have two ovaries, this is not the case in all species. In most birds and in platypuses , the right ovary never matures, so that only the left is functional. (Exceptions include the kiwi and some, but not all raptors , in which both ovaries persist.   ) In some elasmobranchs, only the right ovary develops fully. In the primitive jawless fish , and some teleosts, there is only one ovary, formed by the fusion of the paired organs in the embryo. 
Many hormones and their structural and functional analogs are used as medication . The most commonly prescribed hormones are estrogens and progestogens (as methods of hormonal contraception and as HRT ),  thyroxine (as levothyroxine , for hypothyroidism ) and steroids (for autoimmune diseases and several respiratory disorders ). Insulin is used by many diabetics . Local preparations for use in otolaryngology often contain pharmacologic equivalents of adrenaline , while steroid and vitamin D creams are used extensively in dermatological practice.