part of part of develops_from female reproductive system gonad female gonad (...) while it is likely that Urbilateria lacked a complex somatic reproductive system, it is at present impossible to speculate on whether or not it possessed a true gonad, let alone any other somatic adaptations for reproduction (reference 1); Examination of different vertebrate species shows that the adult gonad is remarkably similar in its morphology across different phylogenetic classes. Surprisingly, however, the cellular and molecular programs employed to create similar organs are not evolutionarily conserved (reference 2).[uncertain][VHOG] AAO:0000371 BILA:0000125 BSA:0000080 BTO:0000975 CALOHA:TS-0730 EFO:0000973 EHDAA2:0001360 EHDAA:8124 EMAPA:17962 EV:0100111 Either of paired female reproductive organs involved in production of ova and female sex hormones.[AAO] FBbt:00004865 FMA:7209 Female reproductive organ.[TAO] GAID:367 MA:0000384 MESH:D010053 MIAA:0000125 OpenCyc:Mx4rvVi9QJwpEbGdrcN5Y29ycA Ovaries of some kind are found in the female reproductive system of many animals that employ sexual reproduction, including invertebrates. However, they develop in a very different way in most invertebrates than they do in vertebrates, and are not truly homologous. Many of the features found in human ovaries are common to all vertebrates, including the presence of follicular cells, tunica albuginea, and so on. However, many species produce a far greater number of eggs during their lifetime than do humans, so that, in fish and amphibians, there may be hundreds, or even millions of fertile eggs present in the ovary at any given time. In these species, fresh eggs may be developing from the germinal epithelium throughout life. Corpora lutea are found only in mammals, and in some elasmobranch fish; in other species, the remnants of the follicle are quickly resorbed by the ovary. In birds, reptiles, and monotremes, the egg is relatively large, filling the follicle, and distorting the shape of the ovary at maturity. Amphibians and reptiles have no ovarian medulla; the central part of the ovary is a hollow, lymph-filled space. The ovary of teleosts is also often hollow, but in this case, the eggs are shed into the cavity, which opens into the oviduct. Although most normal female vertebrates have two ovaries, this is not the case in all species. In birds and platypuses, the right ovary never matures, so that only the left is functional. In some elasmobranchs, the reverse is true, with only the right ovary fully developing. In the primitive jawless fish, and some teleosts, there is only one ovary, formed by the fusion of the paired organs in the embryo TAO:0000403 UBERON:0000992 UMLS:C0029939 VHOG:0000251 XAO:0000258 ZFA:0000403 female organism genitalia gonad female organism genitalia gonada female organism reproductive system gonad female organism reproductive system gonada female reproductive system gonad female reproductive system gonada genitalia of female organism gonad genitalia of female organism gonada gonad of female organism genitalia gonad of female organism reproductive system gonad of female reproductive system gonad of genitalia of female organism gonad of reproductive system of female organism gonada of female organism genitalia gonada of female organism reproductive system gonada of female reproductive system gonada of genitalia of female organism gonada of reproductive system of female organism ovarian ovaries ovarium ovary ovum-producing ovary reproductive system of female organism gonad reproductive system of female organism gonada the gonad of a female organism which contains germ cells uberon female reproductive organ indifferent gonad