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For other uses, see Penis (disambiguation).
Not to be confused with Peanuts or Penix.
This article is about penises of animals in general. For the human organ, see Human penis.
"Penile" and "Penes" redirect here. For the community, see Penile, Louisville. For other uses, see Penes (disambiguation).

Penis
Penis of an Asian elephant
Details
PrecursorGenital tubercle (amniotes)
SystemReproductive system, sometimes with the genitourinary system
Identifiers
Latinpenis
Anatomical terminology

A penis (/ˈpiːnɪs/; pl.: penises or penes) is a male sex organ that is used to inseminate female or hermaphrodite animals during copulation.[1][2] Such organs occur in both vertebrates and invertebrates, but not in all male animals.

The term penis applies to many intromittent organs, but not to all. As an example, the intromittent organ of most Cephalopoda is the hectocotylus, a specialized arm, and male spiders use their pedipalps. Even within the Vertebrata, there are morphological variants with specific terminology, such as hemipenes.

Etymology

The word "penis" is taken from the Latin word for "tail". Some derive that from Indo-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". The Oxford English Dictionary cites an example of the word yard used in this sense from 1379,[3] and notes that in his Physical Dictionary of 1684, Steven Blankaart defined the word penis as "the Yard, made up of two nervous Bodies, the Channel, Nut, Skin, and Fore-skin, etc."[4] According to Wiktionary, this term meant (among other senses) "rod" or "bar".

As with nearly any aspect of the body involved in sexual or excretory functions, the penis is the subject of many slang words and euphemisms for it, a particularly common and enduring one being "cock". See WikiSaurus:penis for a list of alternative words for penis.

The Latin word "phallus" (from Greek φαλλος) is sometimes used to describe the penis, although "phallus" originally was used to describe representations, pictorial or carved, of the penis.[5]

Evolution and function

A tiger's penis is aimed backward during urination. Tigers scent-mark their territories with pheromones in urine.[6]
A tiger's penis is aimed backward during urination. Tigers scent-mark their territories with pheromones in urine.[6]
Dogs mark their territories with urine and secretions from the preputial glands in front of the penis.[7]
Dogs mark their territories with urine and secretions from the preputial glands in front of the penis.[7]

The external genital organs appeared in the Devonian, about 410 million years ago, when tetrapods began to abandon the aquatic environment.[8] In fact, the necessity to overcome the absence of a liquid phase in which to release the gametes was achieved through the transition to internal fertilization.

Among amniotes, the development of an erectile penis occurred independently for mammals, squamates (lizards and snakes), testudines (turtles), and archosaurs (crocodiles and birds).

Over time, birds have lost this organ, with the exception of Paleognathae and Anseriformes.[9]

The penis is an intromittent organ used to transfer sperm into the female genital tract for potential fertilization and, in the case of placentals, also for the excretion of urine.[10][11] 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 amniotes (mammals, birds and reptiles) likely possessed a penis.[12]

Vertebrates

Birds

Male ducks have a corkscrew-shaped penis while female ducks have corkscrew vaginas with many blind pockets designed for difficult penetration and to prevent becoming pregnant.[13] This reduced the likelihood of fertilization by unwanted aggressors in favor of fitter mates.

Most male birds (e.g., roosters and turkeys) have a cloaca (also present on the female), but not a penis. Among bird species with a penis are paleognaths (tinamous and ratites)[14] and Anatidae (ducks, geese and swans).[15] A bird penis is different in structure from mammal penises, being an erectile expansion of the cloacal wall (in ducks) and being erected by lymph, not blood.[16] It is usually partially feathered and in some species features spines and brush-like filaments, and in a flaccid state, curls up inside the cloaca.

Mammals

Penis of a hamadryas baboon
Penis of a horse
Penis of a cat
Penis of a dog (Great Dane)
Penis of a giraffe

As with any other bodily attribute, the length and girth of the penis can be highly variable between mammals of different species.[17][18] In many mammals, the penis is retracted into a prepuce when not erect. Mammals have either musculocavernous penises, which expand while erect, or fibroelastic penises, which become erect by straightening without expanding.[19] Preputial glands are present in some prepuces. The penis bears distal part of the urethra in placental mammals.[10] The perineum of testicond mammals separates the anus and 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:[20]

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).

Genitorinary system of a male raccoon (Procyon lotor)

Canine penises have a structure at the base called the bulbus glandis.[21][22] 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 closely resembles the male hyena's penis, but can be distinguished from the male's genitalia by its greater thickness and more rounded glans.[23] Domestic cats have barbed penises, with about 120–150 one millimetre long backwards-pointing spines.[24]

Marsupials usually have bifurcated penises[25] that are retracted into a preputial sheath in the male's urogenital sinus when not erect.[26] Monotremes and marsupial moles are the only mammals in which the penis is located inside the cloaca.[27][28]

Reptiles

Male turtles and crocodiles have a penis, while male specimens of the reptile order Squamata, which are snakes and lizards, have two paired organs called hemipenes. Tuataras must use their cloacae for reproduction.[29] Due to evolutionary convergence, turtle and mammal penises have a similar structure.[30]

Fish

In some fish, the gonopodium, andropodium, and claspers are intromittent organs (to introduce sperm into the female) developed from modified fins.[31]

Invertebrates

The spine-covered penis of Callosobruchus analis, a bean weevil

In male insects, the structure analogous to a penis is known as aedeagus. The male copulatory organ of various lower invertebrate animals is often called the cirrus.[32]

In 2010, entomologist Charles Linehard described a new genus of barkflies 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.[33] A similar female structure has also been described in the closely related Afrotrogla.[34] Scientists who study these insects have occasionally called the gynosome a "female penis"[35][36] and insisted to drop the definition of penis as "the male copulatory organ".[37] Motivations for using the term “female penis” include that such a term "is easier to understand and much more eye-catching"[38] and that the gynosome have "analogous features" with male penises.[37] 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".[39]

Heraldry

Main article: Pizzle

Pizzles are represented in heraldry, where the adjective pizzled (or vilené[40]) indicates that part of an animate charge's anatomy, especially if coloured differently.

See also

References

Citations

  1. ^ Janet Leonard; Alex Cordoba-Aguilar R (18 June 2010). The Evolution of Primary Sexual Characters in Animals. Oxford University Press. ISBN 978-0-19-971703-3. Archived from the original on 11 October 2013. Retrieved 20 July 2013.
  2. ^ Schmitt, V.; Anthes, N.; Michiels, N. K. (2007). "Mating behaviour in the sea slug Elysia timida (Opisthobranchia, Sacoglossa): hypodermic injection, sperm transfer and balanced reciprocity". Frontiers in Zoology. 4: 17. doi:10.1186/1742-9994-4-17. ISSN 1742-9994. PMC 1934903. PMID 17610714.
  3. ^ Basu, S. C. (2011). Male Reproductive Dysfunction. JP Medical Ltd. p. 101. ISBN 9789350252208.
  4. ^ Simpson, John, ed. (1989). "penis, n.". Oxford English Dictionary (second ed.). Oxford University Press. ISBN 978-0-19-861186-8.[dead link]
  5. ^ "Online Etymology Dictionary". Etymonline.com. Archived from the original on 2011-06-06. Retrieved 2011-05-28.
  6. ^ Watson, Lyall (2000-04-17). Jacobson's Organ: And the Remarkable Nature of Smell. W. W. Norton & Company. ISBN 978-0-393-24493-9.
  7. ^ Mech, L. David; Boitani, Luigi, eds. (2003). Wolves: Behaviour, Ecology and Conservation. University of Chicago Press. ISBN 0-226-51696-2.
  8. ^ Dunlop, Jason A.; Penney, David. Fossil Arachnids. Siri Scientific Press. p. 44. ISBN 978-0-95677-954-0.
  9. ^ Cordoba-Aguilar, Alex; Leonard, Janet (2010). The Evolution of Primary Sexual Characters in Animals. Oxford University Press. pp. 216–221. ISBN 978-0-19971-703-3.
  10. ^ a b Marvalee H. Wake (15 September 1992). Hyman's Comparative Vertebrate Anatomy. University of Chicago Press. p. 583. ISBN 978-0-226-87013-7. Archived from the original on 31 December 2013. Retrieved 23 July 2013.
  11. ^ Feldhamer, George A. (2007-09-07). Mammalogy: Adaptation, Diversity, Ecology. JHU Press. ISBN 978-0-8018-8695-9.
  12. ^ Sanger TJ, Gredler ML, Cohn MJ (October 2015). "Resurrecting embryos of the tuatara, Sphenodon punctatus, to resolve vertebrate phallus evolution". Biology Letters. 11 (10): 20150694. doi:10.1098/rsbl.2015.0694. PMC 4650183. PMID 26510679.
  13. ^ Brennan, Patricia L. R.; Clark, Christopher J.; Prum, Richard O. (2010-05-07). "Explosive eversion and functional morphology of the duck penis supports sexual conflict in waterfowl genitalia". Proceedings of the Royal Society B: Biological Sciences. 277 (1686): 1309–1314. doi:10.1098/rspb.2009.2139. ISSN 0962-8452. PMC 2871948. PMID 20031991.
  14. ^ Julian Lombardi (1998). Comparative Vertebrate Reproduction. Springer. ISBN 978-0-7923-8336-9. Archived from the original on 26 March 2014. Retrieved 5 December 2012.
  15. ^ MobileReference (15 December 2009). The Illustrated Encyclopedia of European Birds: An Essential Guide to Birds of Europe. MobileReference. ISBN 978-1-60501-557-6. Archived from the original on 26 March 2014. Retrieved 5 December 2012.
  16. ^ Frank B. Gill (6 October 2006). Ornithology. Macmillan. pp. 414–. ISBN 978-0-7167-4983-7. Archived from the original on 7 January 2014. Retrieved 5 December 2012.
  17. ^ Tim Birkhead (2000). Promiscuity: An Evolutionary History of Sperm Competition. Harvard University Press. p. 102. ISBN 978-0-674-00666-9. Archived from the original on 26 March 2014. Retrieved 23 July 2013.
  18. ^ Virginia Douglass Hayssen; Ari Van Tienhoven (1993). Asdell's Patterns of Mammalian Reproduction: A Compendium of Species-Specific Data. Cornell University Press. ISBN 978-0-8014-1753-5. Retrieved 23 July 2013.
  19. ^ Chenoweth, Peter J.; Lorton, Steven P. (2022-02-03). Manual of Animal Andrology. CABI. ISBN 978-1-78924-350-5.
  20. ^ William O. Reece (2009-03-04). Functional Anatomy and Physiology of Domestic Animals. John Wiley & Sons. ISBN 9780813814513. Archived from the original on 2018-03-20.
  21. ^ Susan Long (2006). Veterinary Genetics and Reproductive Physiology. Churchill Livingstone Elsevier. ISBN 978-0-7506-8877-2. Archived from the original on 2014-03-26. Retrieved 2013-11-08.
  22. ^ R. F. Ewer (1998). The Carnivores. Cornell University Press. p. 116. ISBN 978-0-8014-8493-3. Archived from the original on 26 March 2014. Retrieved 23 July 2013.
  23. ^ Glickman, SE; Cunha, GR; Drea, CM; Conley, AJ; Place, NJ (2006). "Mammalian sexual differentiation: lessons from the spotted hyena" (PDF). Trends Endocrinol Metab. 17 (9): 349–356. doi:10.1016/j.tem.2006.09.005. PMID 17010637. S2CID 18227659. Archived (PDF) from the original on 2013-02-22.
  24. ^ Aronson, L. R.; Cooper, M. L. (1967). "Penile spines of the domestic cat: their endocrine-behavior relations" (PDF). Anat. Rec. 157 (1): 71–8. doi:10.1002/ar.1091570111. PMID 6030760. S2CID 13070242. Archived from the original (PDF) on 2017-06-20.
  25. ^ Tyndale-Biscoe, C. Hugh; Renfree, Marilyn (1987-01-30). Reproductive Physiology of Marsupials. Cambridge University Press. ISBN 978-0-521-33792-2.
  26. ^ Armati, Patricia J.; Dickman, Chris R.; Hume, Ian D. (2006-08-17). Marsupials. Cambridge University Press. ISBN 978-1-139-45742-2.
  27. ^ Gadow, H. On the systematic position of Notoryctes typhlops. Proc. Zool. Soc. London 1892, 361–370 (1892).
  28. ^ 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.
  29. ^ Lutz, Dick (2005), Tuatara: A Living Fossil, Salem, Oregon: DIMI PRESS, ISBN 0-931625-43-2
  30. ^ Kelly, D. A. (2004). "Turtle and mammal penis designs are anatomically convergent". Proceedings. Biological Sciences. 271 (Suppl 5): S293–S295. doi:10.1098/rsbl.2004.0161. PMC 1810052. PMID 15503998.
  31. ^ Ruschenberger, William Samuel Waithman (1846). Elements of Herpetology, and of Ichthyology: Prepared for the Use of Schools and Colleges. Grigg & Elliot. pp. 129–145.
  32. ^ "Penis | Description, Anatomy, & Physiology | Britannica". Encyclopædia Britannica. January 2024.
  33. ^ Lienhard, Charles; Oliveira do Carmo, Thais; Lopes Ferreira, Rodrigo (2010). "A new genus of Sensitibillini from Brazilian caves (Psocodea: 'Psocoptera': Prionoglarididae)". Revue Suisse de Zoologie. 117 (4): 611–635. doi:10.5962/bhl.part.117600. ISSN 0035-418X. Archived from the original on 2014-11-03.
  34. ^ 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
  35. ^ Yoshizawa, Kazunori; Ferreira, Rodrigo L.; Kamimura, Yoshitaka; Lienhard, Charles (2014). "Female Penis, Male Vagina, and Their Correlated Evolution in a Cave Insect". Current Biology. 24 (9): 1006–10. doi:10.1016/j.cub.2014.03.022. hdl:2115/56857. ISSN 0960-9822. PMID 24746797.
  36. ^ 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
  37. ^ a b Yoshizawa K, Ferreira R.L., Kamimura Y & Lienhard C. "A Transgender Brazilian Cave Insect". The Winnower 3/9/2014
  38. ^ Hollier J & Hollier A. (2020). "The retired taxonomist and the gynosome – the discovery of the female penis". Antenna 44(3): p. 122-125
  39. ^ 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
  40. ^ Rietstap, J. B. (1884). "Armorial général; précédé d'un Dictionnaire des termes du blason". G. B. van Goor zonen: XXXI. Vilené: se dit un animal qui a la marque du sexe d'un autre émail que le corps {{cite journal}}: Cite journal requires |journal= (help)

General and cited references

Horses

Marsupials

Other animals

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