sex organ sex organ a sex organ, also known as a reproductive organ, is a part of an organism that is involved in sexual reproduction. sex organs constitute the primary sex characteristics of an organism. sex organs are responsible for producing and transporting gametes, as well as facilitating fertilization and supporting the development and birth of offspring. sex organs are found in many species of animals and plants, with their features varying depending on the species. the sex organs of the green algae chara are the male antheridia (red) and female archegonia (brown). sex organs are typically differentiated into male and female types. in humans, the male sex organs include the testes, penis, and prostate gland; the female sex organs include the ovaries, fallopian tubes, uterus, cervix, vagina, and vulva. in animals (including humans), the testis in the male and the ovary in the female are called the primary sex organs. all other sex-related organs are called secondary sex organs, divided between internal and external sex organs. external sex organs include the genitals or external genitalia, visible at birth in both sexes. in plants, male reproductive structures include stamens in flowering plants, which produce pollen. female reproductive structures, such as pistils in flowering plants, produce ovules and receive pollen for fertilization. mosses, ferns, and some similar plants have gametangia for reproductive organs, which are part of the gametophyte. the flowers of flowering plants produce pollen and egg cells, but the sex organs themselves are inside the gametophytes within the pollen and the ovule. coniferous plants likewise produce their sexually reproductive structures within the gametophytes contained within the cones and pollen. the cones and pollen are not themselves sexual organs. together, the sex organs constitute an organism's reproductive system. terminology the primary sex organs are the gonads, a pair of sex organs, which diverge into testes following male development or into ovaries following female development. as primary sex organs, gonads generate reproductive gametes containing inheritable dna. they also produce most of the primary hormones that affect sexual development, and regulate other sexual organs and sexually differentiated behaviors. secondary sex organs are the rest of the reproductive system, whether internal or external. the latin term genitalia, sometimes anglicized as genitals, is used to describe the externally visible sex organs: in male mammals, the penis and scrotum; and in female mammals, the vulva and its organs. in general zoology, given the great variety in organs, physiologies, and behaviors involved in copulation, male genitalia are more strictly defined as "all male structures that are inserted in the female or that hold her near her gonopore during sperm transfer"; female genitalia are defined as "those parts of the female reproductive tract that make direct contact with male genitalia or male products (sperm, spermatophores) during or immediately after copulation". evolution it is hard to find a common origin for gonads but, gonads most likely evolved independently several times. at first testes and ovaries evolved due to natural selection. a consensus has emerged that sexual selection represents a primary factor for genital evolution. male genitalia show traits of divergent evolution that are driven by sexual selection. animals mammals further information: mammalian reproductive system and human reproductive system the visible portion of the mammalian genitals for males consists of the scrotum and penis; for females, it consists of the vulva (labia, clitoris, etc.) and vagina. in placental mammals, females have two genital orifices, the vagina and urethra, while males have only one, the urethra. male and female genitals have many nerve endings, resulting in pleasurable and highly sensitive touch. in most human societies, particularly in conservative ones, exposure of the genitals is considered a public indecency. in humans, sex organs include: male female bulbourethral glands epididymis penis foreskin frenulum of penis glans penis prostate scrotum seminal vesicles testicles an image of human male external sex organs (shaved pubic hair) bartholin's glands fallopian tubes ovaries skene's gland uterus cervix vagina vulva hymen clitoris clitoral frenulum clitoral glans (glans clitoridis) clitoral hood labia labia majora labia minora frenulum of labia minora an image of human female external sex organs (shaved pubic hair) development main article: development of the reproductive system