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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.
Sex organs are typically differentiated into male and female types.
In animals (including humans), the male sex organs include the , epididymis, and penis; the female sex organs include the clitoris, Ovary, , and vagina. The testicle in the male and the ovary in the female are called the primary sex organs. All other sex-related organs are known as secondary sex organs. The outer parts are known as the genitals or external genitalia, visible at birth in both sexes, while the inner parts are referred to as internal genitalia, which in both sexes, are always hidden.
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. , , and some similar plants have gametangia for reproductive organs, which are part of the gametophyte. The of produce pollen and , but the sex organs themselves are inside the gametophytes within the pollen and the ovule. Conifer likewise produce their sexually reproductive structures within the gametophytes contained within the Conifer cone and pollen. The cones and pollen are not themselves sexual organs.
Together, the sex organs constitute an organism's reproductive system.
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 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".Eberhard, W.G., 1985. Sexual Selection and Animal Genitalia. Harvard University Press
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.
Male placental mammals urination and ejaculation through one urinary meatus in the penis, while females have two separate Vaginal opening and urethral openings. 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:
External
Internal
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The development of the internal and external reproductive organs is determined by hormones produced by certain fetal gonads (ovaries or testicles) and the cells' response to them. The initial appearance of the fetus genitalia looks female-like: a pair of urogenital folds with a small protuberance in the middle, and the urethra behind the protuberance. If the fetus has testes and the testes produce testosterone, and if the cells of the genitals respond to the testosterone, the outer urogenital folds swell and fuse in the midline to produce the scrotum; the protuberance grows larger and straighter to form the penis; the inner urogenital swellings grow, wrap around the penis, and fuse in the midline to form the penile raphe. Each organ/body part in one sex has a homologous counterpart.
The process of sexual differentiation includes the development of secondary sexual characteristics, such as patterns of pubic and facial hair and female breasts that emerge at puberty.
Because of the strong [[sexual selection]] affecting the structure and function of genitalia, they form an organ system that evolves rapidly.Hosken, David J., and Paula Stockley."[http://www.sexologia.ulusofona.pt/biblio/Indice_files/Sexual%20selection%20and%20genital%20evolution.pdf Sexual selection and genital evolution]." Trends in Ecology & Evolution 19.2 (2004): 87-93.Arnqvist, Göran. "[http://heart.sdsu.edu/~website/biology_307/pdfs/genitalia.pdf Comparative evidence for the evolution of genitalia by sexual selection]." Nature 393.6687 (1998): 784.Schilthuizen, M. 2014. [https://books.google.com/books?id=xqM7AgAAQBAJ&dq=nature%27s+nether+regions&pg=PT2 Nature's Nether Regions: What the Sex Lives of Bugs, Birds, and Beasts Tell Us About Evolution, Biodiversity, and Ourselves] . Penguin USA A great variety of genital form and function may therefore be found among animals.
Penile and clitoral structures are present in some birds and many reptiles.
Sexing teleost fish is determined by the shape of a fleshy tube behind the anus known as genital papilla.
The life cycle of involves alternation of generations between a sporophyte and a haploid gametophyte. The gametophyte produces sperm or egg cells by mitosis. The sporophyte produces spores by meiosis, which in turn develop into gametophytes. Any sex organs that are produced by the plant will develop on the gametophyte. The , which include and , have small gametophytes that develop inside the pollen grains (male) and the ovule (female).
Sexual reproduction in involves the union of the male and female germ cells, sperm and egg cells respectively. Pollen is produced in and is carried to the pistil or carpel, which has the ovule at its base where fertilization can take place. Within each pollen grain is a male gametophyte, which consists of only three cells. In most flowering plants, the female gametophyte within the ovule consists of only seven cells. Thus there are no sex organs as such.
Similar gametangia that are similar are known as isogametangia. While male and female gametangia are known as heterogametangia, which occurs in the majority of fungi.
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