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A penis (; : penises or penes) is a sex organ used by male and hermaphrodite animals to copulate, and by male placental mammals to Urination.
The term penis applies to many intromittent organs of and , but not to all. As an example, the intromittent organ of most is the hectocotylus, a specialized arm, and male spiders use their . Even within the Vertebrata, there are morphological variants with specific terminology, such as Hemipenis.
As with nearly any aspect of the body involved in sexual or excretory functions, the penis is the subject of many slang words and for it, a particularly common and enduring one being "cock". See for a list of alternative words for penis.
The Latin word "phallus" (from Greek language φαλλος) is sometimes used to describe the penis, although "phallus" originally was used to describe representations, pictorial or carved, of the penis.
Among amniotes, the development of an erectile penis occurred independently for , Squamata ( and snakes), Turtle (turtles), and (crocodiles and birds).
Over time, birds have lost this organ, with the exception of Paleognathae and Anseriformes.
The penis is an intromittent organ used to transfer sperm into the female genital tract (i.e., vagina or cloaca) for potential fertilization. The penises of different animal groups are not homologous with each other, but were created several times independently of each other in the course of evolution.
An erection is the stiffening and rising of the penis, which occurs during sexual arousal, though it can also happen in non-sexual situations. During ejaculation, a series of muscular contractions delivers semen, containing male gametes known as sperm cells or spermatozoa, from the penis. Ejaculation is usually accompanied by orgasm.
The last common ancestor of all living (mammals, birds and reptiles) likely possessed a penis.
Marsupial and Placentalia expel both urine and semen from the urethra through the penis. A bone called the baculum is present in most placentals but absent in humans, cattle and horses.
In mammals, the penis is divided into three parts:
The internal structures of the penis consist mainly of cavernous, erectile tissue, which is a collection of blood sinusoids separated by sheets of connective tissue (trabeculae).
Human penis have a large internal portion but are much more externally visible when flaccid than the penises of hooved animals. The size of the penis and protrusion of the testicles change naturally with temperature for protection.
have a structure at the base called the bulbus glandis. During copulation, the spotted hyena inserts his penis through the female's pseudo-penis instead of directly through the vagina, which is blocked by the false scrotum. The pseudo-penis and pseudo-scrotum, which are actually a virilization vulva, closely resemble the male hyena's genitalia, but can be distinguished from the male by the female's greater thickness and more rounded glans. Domestic cats have barbed penises, with about 120–150 one millimetre long penile spines.
usually have bifurcated penises that are retracted into a preputial sheath in the male's urogenital sinus when not erect. and are the only mammals in which the penis is located inside the cloaca.Gadow, H. On the systematic position of Notoryctes typhlops. Proc. Zool. Soc. London 1892, 361–370 (1892).Riedelsheimer, B., Unterberger, P., Künzle, H. and U. Welsch. 2007. Histological study of the cloacal region and associated structures in the hedgehog tenrec Echinops telfairi. Mammalian Biology 72(6): 330-341.
In male , the structure analogous to a penis is known as an aedeagus. The male copulatory organ of various lower invertebrate animals is often called the cirrus.
In 2010, entomologist Charles Linehard described a new genus of Psocoptera called Neotrogla. Species of this genus have sex-reversed genitalia: females have penis-like organs called gynosomes that are inserted into vagina-like openings of males during mating. A similar female structure has also been described in the closely related Afrotrogla.Yoshizawa K, Ferreira R.L., Yao I, Lienhard C & Kamimura Y. "Independent origins of female penis and its coevolution with male vagina in cave insects (Psocodea: Prionoglarididae)". Biology Letters 14(11): doi.org/10.1098/rsbl.2018.0533 Scientists who study these insects have occasionally called the gynosome a "female penis"Yoshizawa K, Ferreira R.L., Lienhard C & Kamimura Y. (2019). "Why Did a Female Penis Evolve in a Small Group of Cave Insects?". BioEssays 41(6): doi.org/10.1002/bies.201900005 and insisted to drop the definition of penis as "the male copulatory organ".Yoshizawa K, Ferreira R.L., Kamimura Y & Lienhard C. "A Transgender Brazilian Cave Insect". The Winnower 3/9/2014 Motivations for using the term "female penis" include that such a term "is easier to understand and much more eye-catching"Hollier J & Hollier A. (2020). "The retired taxonomist and the gynosome – the discovery of the female penis". Antenna 44(3): p. 122-125 and that the gynosome have "analogous features" with male penises. Meanwhile, critics have argued that it does not fit the intromittent organ definition of "a structure that enters the female genital tract and deposits sperm".Hayssen V. (2020). "Misconceptions about Conception and Other Fallacies: Historical Bias in Reproductive Biology". Integrative and Comparative Biology 60(3): p. 683-791: doi.org/10.1093/icb/icaa035
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