Copulation (zoology) in the context of "Intromittent organ"

Penile–vaginal intercourse, or vaginal intercourse, is the insertion of an erect penis into a vagina. It is the primary form of copulation in mammals and a form of penetrative sexual intercourse in human sexuality. Synonyms are: vaginal sex, coitus (Latin: coitus per vaginam), (in elegant colloquial language) intimacy, or (poetic) lovemaking; some of which are used for other forms of intercourse as well. Cohabitation is a related term describing a living arrangement.

Various sex positions can be used. Following insertion, additional stimulation is often achieved through rhythmic pelvic thrusting or a gyration of the hips, among other techniques. The biological imperative is to achieve male ejaculation so that sperm can enter the female reproductive tract and fertilize the egg, thus beginning the next stage in human reproduction, pregnancy.

Sexual reproduction is a type of reproduction that involves a complex life cycle in which a gamete (haploid reproductive cells, such as a sperm or egg cell) with a single set of chromosomes combines with another gamete to produce a zygote that develops into an organism composed of cells with two sets of chromosomes (diploid). This is typical in animals, though the number of chromosome sets and how that number changes in sexual reproduction varies, especially among plants, fungi, and other eukaryotes.

In placental mammals, sperm cells exit the penis through the male urethra and enter the vagina during copulation, while egg cells enter the uterus through the oviduct. Other vertebrates of both sexes possess a cloaca for the release of sperm or egg cells.

In biology, mating is the pairing of either opposite-sex or hermaphroditic organisms for the purposes of sexual reproduction. Fertilization is the fusion of two gametes. Copulation is the union of the sex organs of two sexually reproducing animals for insemination and subsequent internal fertilization. Mating may also lead to external fertilization, as seen in amphibians, bony fishes and plants. For most species, mating is between two individuals of opposite sexes. However, for some hermaphroditic species, copulation is not required because the parent organism is capable of self-fertilization (autogamy); for example, banana slugs.

The term mating is also applied to related processes in bacteria, archaea and viruses. Mating in these cases involves the pairing of individuals, accompanied by the pairing of their homologous chromosomes and then exchange of genomic information leading to formation of recombinant progeny (see mating systems).

Animal sexual behaviour takes many different forms, including within the same species. Common mating or reproductively motivated systems include monogamy, polygyny, polyandry, polygamy and promiscuity. Other sexual behaviour may be reproductively motivated (e.g. sex apparently due to duress or coercion and situational sexual behaviour) or non-reproductively motivated (e.g. homosexual sexual behaviour, bisexual sexual behaviour, cross-species sex, sexual arousal from objects or places, sex with dead animals, etc.).

When animal sexual behaviour is reproductively motivated, it is often termed mating or copulation; for most non-human mammals, mating and copulation occur at oestrus (the most fertile period in the mammalian female's reproductive cycle), which increases the chances of successful impregnation. Some animal sexual behaviour involves competition, sometimes fighting, between multiple males. Females often select males for mating only if they appear strong and able to protect themselves. The male that wins a fight may also have the chance to mate with a larger number of females and will therefore pass on his genes to their offspring.

A cloaca (/kloʊˈeɪkə/ kloh-AY-kə), pl.: cloacae (/kloʊˈeɪsi/ kloh-AY-see or /kloʊˈeɪki/ kloh-AY-kee), or vent, is the rear orifice that serves as the only opening for the digestive (rectum), reproductive, and urinary tracts (if present) of many vertebrate animals. All amphibians, reptiles, birds, cartilaginous fish and a few mammals (monotremes, afrosoricids, and marsupial moles) have this orifice, from which they excrete both urine and feces; this is in contrast to most placental mammals, which have separate orifices for evacuation and reproduction. Excretory openings with analogous purpose in some invertebrates are also sometimes called cloacae. Mating through the cloaca is called cloacal copulation and cloacal kissing.

The cloacal region is also often associated with a secretory organ, the cloacal gland, which has been implicated in the scent-marking behavior of some reptiles, marsupials, amphibians, and monotremes.

Spawn is the eggs and sperm released or deposited into water by aquatic animals. As a verb, to spawn refers to the process of freely releasing eggs and sperm into a body of water (fresh or marine); the physical act is known as spawning. The vast majority of aquatic and amphibious animals reproduce through spawning. These include the following groups:

• Bony fishes
• Crustaceans (such as crabs, shrimps, etc.)
• Mollusks (such as oysters, octopus, squid)
• Echinoderms (such as sea urchins, sea stars, sea cucumbers, etc.)
• Amphibians (such as frogs, toads, salamanders, newts)
• Aquatic insects (such as dragonflies, mayflies, mosquitoes)
• Coral, which are living colonies of tiny, aquatic organisms—not plants, as they are sometimes perceived to be. Corals, while appearing sedentary or botanical by nature, actually spawn by releasing clouds of sperm and egg cells into the water column, where the two mix.

As a general rule, aquatic or semiaquatic reptiles, birds, and mammals do not reproduce through spawning, but rather through copulation like their terrestrial counterparts. This is also true of cartilaginous fishes (such as sharks, rays and skates).

In mammals and other animals, the vagina (pl.: vaginas or vaginae) is the elastic, muscular reproductive organ of the female genital tract. In humans, it extends from the vulval vestibule to the cervix (neck of the uterus). The vaginal introitus is normally partly covered by a thin layer of mucosal tissue called the hymen. The vagina allows for copulation and birth. It also channels menstrual flow, which occurs in humans and closely related primates as part of the menstrual cycle.

To accommodate smoother penetration of the vagina during sexual intercourse or other sexual activity, vaginal moisture increases during sexual arousal in human females and other female mammals. This increase in moisture provides vaginal lubrication, which reduces friction. The texture of the vaginal walls creates friction for the penis during sexual intercourse and stimulates it toward ejaculation, enabling fertilization. Along with pleasure and bonding, women's sexual behavior with other people can result in sexually transmitted infections (STIs), the risk of which can be reduced by recommended safe sex practices. Other health issues may also affect the human vagina.

Breeding pair is a pair of animals which cooperate over time to produce offspring with some form of a bond between the individuals. For example, many birds mate for a breeding season or sometimes for life. They may share some or all of the tasks involved: for example, a breeding pair of birds may split building a nest, incubating the eggs and feeding and protecting the young. The term is not generally used when a male has a harem of females, such as with mountain gorillas.

True breeding pairs are usually found only in vertebrates, but there are notable exceptions, such as the Lord Howe Island stick insect. True breeding pairs are rare in amphibians or reptiles, although the Australian Shingleback is one exception with long-term pair-bonds. Some fish form short term pairs and the French angelfish is thought to pair-bond over a long term. True breeding pairs are quite common in birds. Breeding pair arrangements are rare in mammals, where the prevailing patterns are either that the male and female only meet for copulation (e.g. brown bear) or that dominant males have a harem of females (e.g. walrus).