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The termpenis applies to manyintromittent organs, but not to all. As an example, the intromittent organ of mostCephalopoda is thehectocotylus, a specialized arm, and male spiders use theirpedipalps. Even within theVertebrata, there are morphological variants with specific terminology, such ashemipenes.
In most species of animals in which there is an organ that might be described as a penis, it has no major function other than intromission, or at least conveying the sperm to the female, but in theplacental mammals, the penis bears thedistal part of theurethra, which discharges bothurine duringurination andsemen during copulation.[3]
Vertebrates
The last common ancestor of all livingamniotes (mammals, birds and reptiles) likely possessed a penis.[4]
Most male birds (e.g.,roosters andturkeys) have acloaca (also present on the female), but not a penis. Among bird species with a penis arepaleognathes (tinamous andratites)[6] andAnatidae (ducks, geese and swans).[7] A bird penis is different in structure frommammal penises, being an erectile expansion of the cloacal wall and being erected bylymph, not blood.[8] It is usually partially feathered and in some species features spines and brush-like filaments, and in flaccid state curls up inside the cloaca.
While most male birds have no external genitalia, male waterfowl (Anatidae) have a phallus. Most birds mate with the males balancing on top of the females and touching cloacas in a "cloacal kiss"; this makesforceful insemination very difficult. The phallus that male waterfowl have evolved everts out of their bodies (in a clockwise coil) and aids in inseminating females without their cooperation.[9] The male waterfowl evolution of a phallus to forcefully copulate with females has led to counteradaptations in females in the form of vaginal structures called dead end sacs and clockwise coils. These structures make it harder for males to achieve intromission. The clockwise coils are significant because the male phallus everts out of their body in a counter-clockwise spiral; therefore, a clockwise vaginal structure would impede forceful copulation. Studies have shown that the longer a male's phallus is, the more elaborate the vaginal structures were.[9]
Duck females have corkscrew vaginas with many blind pockets designed for difficult penetration and to prevent becoming pregnant. This reduced the likelihood of fertilization by unwanted aggressors in favor of fitter mates.
Thelake duck is notable for possessing, in relation to body length, thelongest penis of allvertebrates; the penis, which is typically coiled up in flaccid state, can reach about the same length as the animal himself when fully erect, but is more commonly about half the bird's length.[10][11] It is theorized that the remarkable size of theirspiny penises with bristled tips may have evolved in response to competitive pressure in these highly promiscuous birds, removing sperm from previous matings in the manner of abottle brush. The lake duck has a corkscrew shaped penis.[12]
Male and femaleemus are similar in appearance,[13] although the male's penis can become visible when he defecates.[14]
The male tinamou has a corkscrew shaped penis, similar to those of the ratites and to thehemipenis of some reptiles. Females have a small phallic organ in the cloaca which becomes larger during the breeding season.[15]
Mammals
Wikimedia Commons has media related toMammal penis.
As with any other bodily attribute, the length and girth of the penis can be highly variable betweenmammals of differentspecies.[16][17] In many mammals, the size of a flaccid penis is smaller than itserect size.
A bone called thebaculum is present in most mammals but absent in humans, cattle andhorses.
In mammals, the penis is divided into three parts:[18]
The internal structures of the penis consist mainly of cavernous,erectile tissue, which is a collection ofblood sinusoids separated by sheets ofconnective tissue (trabeculae). Some mammals have a lot of erectile tissue relative to connective tissue, for example horses. Because of this ahorse's penis can enlarge more than abull's penis. Theurethra is on the ventral side of the body of the penis. As a general rule, a mammal's penis is proportional to its body size, but this varies greatly between species – even between closely related ones. For example, an adultgorilla's erect penis is about 4.5 cm (1.8 in) in length; an adultchimpanzee, significantly smaller (in body size) than a gorilla, has a penis size about double that of the gorilla. In comparison, thehuman penis is larger than that of any otherprimate, both in proportion to body size and in absolute terms.[19]
Artiodactyls
The penises of even-toed ungulates are curved in an S-shape when not erect.[20] Inbulls,rams andboars, the sigmoid flexure of the penis straightens out during erection.[21]
When mating, the tip of a malepronghorn's penis is often the first part to touch the female pronghorn.[22] The pronghorn's penis is about 13 cm (5 in) long, and is shaped like an ice pick.[23] The front of a pronghorn's glans penis is relatively flat, while the back is relatively thick.[24] The male pronghorn usuallyejaculates immediately after intromission.[25][26]
The penis of adromedary camel is covered by a triangular penile sheath opening backwards,[27] and is about 60 cm (24 in) long.[28][29] The camelmen often aid the male to enter his penis into the female'svulva, though the male is considered able to do it on his own. Copulation time ranges from 7 to 35 minutes, averaging 11–15 minutes.[30][31]
Bullshave a fibro-elastic penis. Given the small amount of erectile tissue, there is little enlargement after erection. The penis is quite rigid when non-erect, and becomes even more rigid during erection. Protrusion is not affected much by erection, but more by relaxation of theretractor penis muscle and straightening of thesigmoid flexure.[32][18][33]
The male genitalia ofmouse deer are similar to those of pigs.[34] A boar's penis, which rotates rhythmically during copulation,[35] is about 46 cm (18 in) long, and ejaculates about a pint of semen.[36] Wild boars have a roughly egg-sized sack near the opening of the penis, which collects urine and emits a sharp odour. The purpose of this is not fully understood.[37]
A stag's penis forms an S-shaped curve when it is not erect, and is retracted into its sheath by the retractor penis muscle.[38] Some deer speciesspray urine on their bodies by urinating from an erect penis.[39] One type of scent-marking behavior in elk is known as "thrash-urination,[40][41] which typically involves palpitation of the erect penis.[41][42][43] A male elk's urethra points upward so that urine is sprayed almost at a right angle to the penis.[41] Asambar stag will mark himself byspraying urine directly in the face with a highly mobile penis, which is oftenerect during itsrutting activities.[44]Red deer stags often have erect penises during combat.[45]
Wikimedia Commons has media related toCetacea penis.
Cetaceans' reproductive organs are located inside the body. Malecetaceans (whales, dolphins, and porpoises) have two slits, the genital groove concealing the penis and one further behind for theanus.[46][47][48][49] Cetaceans have fibroelastic penises, similar to those ofArtiodactyla.[50] The tapering tip of the cetacean penis is called thepars intrapraeputialis orterminal cone.[51] Theblue whale has thelargest penis of any organism on the planet, typically measuring 2.4–3.0 m (8–10 ft).[52] Accurate measurements are difficult to take because its erect length can only be observed during mating,[53] which occurs underwater. The penis on aright whale can be up to 2.7 m (8.9 ft) – thetesticles, at up to 2 m (6 ft 7 in) in length, 78 cm (2 ft 7 in) in diameter, and weighing up to 238 kg (525 lb), are also by far the largest of any animal on Earth.[54]On at least one occasion, a dolphin towed bathers through the water by hooking his erect penis around them.[55] Between captive male dolphins—includingbottlenose dolphins andAmazon river dolphins—homosexual behaviour includes rubbing of genitals against each other, which sometimes leads to the males swimming belly to belly, inserting the penis in the other'sgenital slit and sometimes anus.[56][57]
Tapirs have exceptionally long penises relative to their body size.[58][59][60][61] The glans of the Malayan tapir resembles a mushroom, and is similar to the glans of the horse.[62] The penis of theSumatran rhinoceros contains two lateral lobes and a structure called theprocessus glandis.[63]
During copulation, the spotted hyena inserts his penis throughthe female's pseudo-penis instead of directly through thevagina, which is blocked by the false scrotum and testicles. Once the female retracts her clitoris, the male enters the female by sliding beneath her, an operation facilitated by the penis' upward angle.[67][68] The pseudo-penis closely resembles the male hyena's penis, but can be distinguished from the male's genitalia by its greater thickness and more roundedglans.[69] In male spotted hyenas, as well as females, the base of the glans is covered withpenile spines.[70][71][72]
The malefossa has an unusually long penis andbaculum (penis bone), reaching to between hisfront legs when erect[78] with backwards-pointing spines along most of its length.[79] The male fossa has scent glands near the penis, with the penile glands emitting a strong odor.[78]
Thebeech marten's penis is larger than the pine marten's, with thebacula of young beech martens often outsizing those of old pine martens.[80]
Raccoons have penis bones which bend at a 90 degree angle at the tip.[81] The extrusibility of a raccoon's penis can be used to distinguish mature males from immature males.[82][83]
Malewalruses possess the largest penis bones of any land mammal, both in absolute size and relative to body size.[84][85]
The adult maleAmerican mink's penis is 5.6 cm (2+1⁄4 in) long, and is covered by asheath. Thebaculum is well-developed, being triangular incross section and curved at the tip.[86]
Bats
Males ofRacey's pipistrelle bat have a long, straight penis with a notch between the shaft and the narrow, egg-shapedglans penis. Near the top, the penis is haired, but the base is almost naked. In thebaculum (penis bone), the shaft is long and narrow and slightly curved.[87] The length of the penis and baculum distinguishP. raceyi from all comparably sized African and Malagasy vespertilionids.[88] In males, penis length is9.6 to 11.8 mm (3⁄8 to15⁄32 in) and baculum length is8.8 to 10.0 mm (11⁄32 to13⁄32 in).[89]
Copulation by malegreater short-nosed fruit bats is dorsoventral and the females lick the shaft or the base of the male's penis, but not the glans which has already penetrated the vagina. While the females do this, the penis is not withdrawn and research has shown a positive relationship between length of the time that the penis is licked and the duration of copulation. Post copulation genital grooming has also been observed.[90]
Rodents
The glans penis of themarsh rice rat is long and robust,[91] averaging7.3 mm (9⁄32 in) long and4.6 mm (3⁄16 in) broad, and the baculum (penis bone) is6.6 mm (1⁄4 in) long.[92] As is characteristic ofSigmodontinae, the marsh rice rat has a complex penis, with the distal (far) end of the baculum ending in three digits.[93] The central digit is notably larger than those at the sides.[91] The outer surface of the penis is mostlycovered by small spines, but there is a broad band of nonspinous tissue. The papilla (nipple-like projection) on the dorsal (upper) side of the penis is covered with small spines, a character the marsh rice rat shares only withOligoryzomys andOryzomys couesi among oryzomyines examined.[94] On the urethral process, located in the crater at the end of the penis,[95] a fleshy process (the subapical lobule) is present; it is absent in all other oryzomyines with studied penes exceptO. couesi andHolochilus brasiliensis.[96] The baculum is deeper than it is wide.[91]
InTransandinomys talamancae, the outer surface of the penis is mostly covered by small spines, but there is a broad band of nonspinous tissue.[97]
Some features of the accessory glands in the male genital region vary amongoryzomyines. InTransandinomys talamancae,[98] a single pair ofpreputial glands is present at the penis. As is usual for sigmodontines, there are two pairs ofventralprostate glands and a single pair ofanterior anddorsal prostate glands. Part of the end of thevesicular gland is irregularly folded, not smooth as in most oryzomyines.[99]
InPseudoryzomys, thebaculum (penis bone) displays large protuberances at the sides. In thecartilaginous part of the baculum, the central digit is smaller than those at the sides.[93]
InDrymoreomys, there are three digits at the tip of the penis, of which the central one is the largest.[100]
InThomasomys ucucha, theglans penis is rounded, short, and small and is superficially divided into left and right halves by a trough at the top and a ridge at the bottom.[101]
The penile morphology of some types ofstrepsirrhineprimates has provided information about their taxonomy.[108] Malegalago species possess very distinctive penile morphology that can be used to classify species.[109][110][111]
Thenorthern greater galago penis is on average18 mm (11⁄16 in) in length, with doubled headed or even tridentate spines pointing towards the body. They are less densely packed than inOtolemur crassicaudatus.[109][110][111] The penis of thering-tailed lemur is nearly cylindrical in shape andis covered in small spines, as well as having two pairs of larger spines on both sides.[112]
The adult male of each vervet monkey species has a pale bluescrotum and a red penis,[113][114] and maleproboscis monkeys have a red penis with a black scrotum.[115]
Malebaboons andsquirrel monkeys sometimes gesture with an erect penis as both a warning of impending danger and a threat to predators.[116][117] In malesquirrel monkeys, this gesture is used for social communication.[118]
In males, the expulsion ofurine from the body is done through the penis. The urethra drains the bladder through theprostate gland, where it is joined by theejaculatory duct, and then onward to the penis.
An erection is the stiffening and rising of the penis, which occurs duringsexual arousal, though it can also happen in non-sexual situations. Ejaculation is the ejecting ofsemen from the penis and is usually accompanied byorgasm. A series of muscular contractions delivers semen, containing malegametes known as sperm cells orspermatozoa, from the penis.
The most common form of genital alteration iscircumcision, the removal of part or all of the foreskin for various cultural, religious, and more rarely medical reasons. There is controversy surrounding circumcision.
As of 2015[update], asystematic review of 15,521 men, who were measured by health professionals rather than themselves, concluded that the average length of anerect human penis is 13.12 cm (5.17 inches) long, while the average circumference of an erect human penis is 11.66 cm (4.59 inches).[119][120]
Marsupials
Most marsupials, except for the two largest species of kangaroos andmarsupial moles[121] (assuming the latter are true marsupials),have a bifurcated penis, separated into two columns, so that the penis has two ends corresponding to the females' two vaginas.[122]
Maleechidnas have a bilaterally symmetrical, rosette-like, four-headed penis.[125] During mating, the heads on one side "shut down" and do not grow in size; the other two are used to release semen into the female's two-branched reproductive tract. The heads used are swapped each time the mammal copulates.[126][127][128] When not in use, the penis is retracted inside a preputial sac in the cloaca. The male echidna's penis is 7 cm (3 in) long when erect, and its shaft is covered withpenile spines.[129] The penis is nearly a quarter of his body length when erect.[130]
The penis of thebush hyrax is complex and distinct from that of the other hyrax genera. It has a short, thin appendage within a cup-like glans penis and measures greater than6 cm (2+1⁄2 in) when erect. Additionally, it has been observed that the bush hyrax also has a greater distance between the anus and preputial opening in comparison to other hyraxes.[131]
An adultelephant has the largest penis of any land animal.[132][self-published source?] An elephant's penis can reach a length of 100 cm (40 in) and a diameter of 16 cm (6 in) at the base.[citation needed] It is S-shaped when fully erect and has a Y-shapedorifice.[133] Duringmusth, a male elephant may urinate with his penis still in thesheath, which causes the urine to spray on thehind legs.[134][135] An elephant's penis is very mobile, being able to move independently of the male's pelvis,[136] and the penis curves forward and upward prior tomounting another elephant.[71]
When the male armadilloChaetophractus villosus issexually aroused, species determination is easier. Its penis can be as long as35 mm (1+1⁄2 in), and usually remains completely withdrawn inside a skin receptacle.[138] Scientists conducting studies on theC. villosus penis muscles revealed this species' very long penis exhibits variability. During its waking hours, it remains hidden beneath a skin receptacle, until it becomes erect and it projects outside in arostral direction.[139]
The spine-covered penis ofCallosobruchus analis, abean weevil
The record for the largest penis size to body size ratio is held by thebarnacle. The barnacle's penis can grow to up to forty times its own body length. This enables them to reach the nearest female for fertilization.
A number of invertebrate species have independently evolved the mating technique oftraumatic insemination where the penis penetrates the female's abdomen, thereby creating a womb into which it deposits sperm. This has been most fully studied inbed bugs.
Somemillipedes have penises. In these species, the penis is simply one or two projections on underneath the thirdbody segment that produce aspermatophore or sperm packet. The act of insemination, however, occurs through specialized legs calledgonopods which collect the spermatophore and insert it into the female.
In maleinsects, the structure analogous to a penis is known asaedeagus. The male copulatory organ of various lower invertebrate animals is often called thecirrus.[142]
Thelesser water boatman'smating call, generated by rubbing the penis against theabdomen, is the loudest sound, relative to body size, in the animal kingdom.
In 2010, entomologist Charles Linehard describedNeotrogla, a new genus ofbarkflies. 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.[143] In 2014, a detailed study of the insects reproductive habits led by Kazunori Yoshizawae confirmed that the organ functions similar to a penis – for example, it swells during sexual intercourse – and is used to extract sperm from the male.[144][145]
Mollusks
The penis in most malecoleoidcephalopods is a long and muscular end of the gonoduct used to transfer spermatophores to a modified arm called ahectocotylus. That, in turn, is used to transfer the spermatophores to the female. In species where the hectocotylus is missing, the penis is long and able to extend beyond the mantle cavity and transfers the spermatophores directly to the female. Deepwater squid have thegreatest known penis length relative to body size of all mobile animals, second in the entire animal kingdom only to certain sessilebarnacles. Penis elongation inOnykia ingens may result in a penis that is as long as the mantle, head and arms combined.[146][147]Giant squid of the genusArchiteuthis are unusual in that they possess both a large penis and modified arm tips, although it is uncertain whether the latter are used for spermatophore transfer.[146]
Etymology
The word "penis" is taken from theLatin word for "tail". Some derive that fromIndo-European*pesnis, and the Greek word πέος = "penis" from Indo-European*pesos. Prior to the adoption of the Latin word in English, the penis was referred to as a "yard". TheOxford English Dictionary cites an example of the wordyard used in this sense from 1379,[148] and notes that in hisPhysical Dictionary of 1684,Steven Blankaart defined the wordpenis as "the Yard, made up of two nervous Bodies, the Channel, Nut, Skin, and Fore-skin, etc."[149] According toWiktionary, this term meant (among other senses) "rod" or "bar".
As with nearly any aspect of the body involved in sexual orexcretory functions, the penis is the subject of manyslang words andeuphemisms for it, a particularly common and enduring one being "cock". SeeWikiSaurus:penis for a list of alternative words for penis.
The Latin word"phallus" (fromGreek φαλλος) is sometimes used to describe the penis, although "phallus" originally was used to describerepresentations, pictorial or carved, of the penis.[150]
Pizzles are represented inheraldry, where the adjectivepizzled (orvilené)[151] indicates that part of an animatecharge's anatomy, especially if coloured differently.
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