Penis

Primary sexual organ of male animals

For other uses, see Penis (disambiguation).

This article is about penises 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).

Not to be confused with Peanut.

Penis

Penis of an Asian elephant

Details
Precursor| Genital tubercle (amniotes)
System| Reproductive system, sometimes with the genitourinary system
Identifiers
Latin| penis
Anatomical terminology

[edit on Wikidata]

A penis (/ˈpiːnɪs/; pl.: penises or penes) is a sex organ through which male and hermaphrodite animals expel semen during copulation,[1][2] and through which male placental mammals and marsupials also urinate.[3][4]

The term penis applies to many intromittent organs of vertebrates and invertebrates, but not to all.[5] 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

[edit]

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,[6] 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."[7] 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.[8]

## Evolution and function

[edit]

A tiger's penis is aimed backward during urination. Tigers scent-mark their territories with pheromones in urine.[9]

The external genital organs appeared in the Devonian, about 410 million years ago, when tetrapods began to abandon the aquatic environment.[10] 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.[11]

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 amniotes (mammals, birds and reptiles) likely possessed a penis.[12]

## Vertebrates

[edit]

### Birds

[edit]

Male ducks have a corkscrew-shaped penis to match the females' corkscrew vaginas. This favors fertilization by fitter mates over unwanted aggressors.[13]

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] The magpie goose in the family Anseranatidae also has a penis. 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

[edit]

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.[4] Preputial glands are present in some prepuces.[3][19] The perineum of testicond mammals (mammals without a scrotum) separates the anus and the penis.

Marsupials[4] and placental mammals expel both urine and semen from the urethra through the penis.[1][3] 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]

* Roots (crura): these begin at the caudal border of the pelvic ischial arch.
* Body: the part of the penis extending from the roots.
* Glans: the free end of the penis and where the urethra opens into in placentals. The penile glans is absent in chimpanzees and bonobos.[21]

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).

Canine penises have a structure at the base called the bulbus glandis.[22][23] 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 masculinized 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.[24] Domestic cats have barbed penises, with about 120–150 one millimetre long backwards-pointing spines.[25]

Marsupials usually have bifurcated penises[26] that are retracted into a preputial sheath in the male's urogenital sinus when not erect.[27] Monotremes and marsupial moles are the only mammals in which the penis is located inside the cloaca.[28][29]

### Reptiles

[edit]

Hemipenes of a gold tegu

Male turtles and crocodilians 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.[30] Due to evolutionary convergence, turtle and mammal penises have a similar structure.[31]

### Fish

[edit]

In some fish, the gonopodium, andropodium, and claspers are intromittent organs (to introduce sperm into the female) developed from modified fins.[32]

## Invertebrates

[edit]

"Female penis" redirects here. For the homologue to the penis in female amniotes, see Clitoris.

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

Harvestmen are the only male arachnids that have a penis.

In male insects, 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.[33]

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.[34] A similar female structure has also been described in the closely related Afrotrogla.[35] Scientists who study these insects have occasionally called the gynosome a "female penis"[36][37] and insisted to drop the definition of penis as "the male copulatory organ".[38] Motivations for using the term "female penis" include that such a term "is easier to understand and much more eye-catching"[39] and that the gynosome have "analogous features" with male penises.[38] 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".[40]

## Heraldry

[edit]

Main article: Pizzle

Pizzles are represented in heraldry, where the adjective pizzled (or vilené[41]) indicates that part of an animate charge's anatomy, especially if coloured differently.

## See also

[edit]

* Diphallia
* Fascinus
* Koteka
* Palpal bulb
* Stamen
* Testicle

## References

[edit]

### Citations

[edit]

1. ^ a b 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. ^ a b c 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.
4. ^ a b c Chenoweth, Peter J.; Lorton, Steven P. (2022-02-03). Manual of Animal Andrology. CABI. ISBN 978-1-78924-350-5.
5. ^ Hosken, David J.; Archer, C. Ruth; House, Clarissa M.; Wedell, Nina (2019). "Penis evolution across species: divergence and diversity". Nature Reviews Urology. 16 (2): 98–106\. doi:10.1038/s41585-018-0112-z. hdl:10871/34696.
6. ^ Basu, S. C. (2011). Male Reproductive Dysfunction. JP Medical Ltd. p. 101\. ISBN 9789350252208.
7. ^ Simpson, John, ed. (1989). "penis, n.". Oxford English Dictionary (second ed.). Oxford University Press. ISBN 978-0-19-861186-8.[dead link]
8. ^ "Online Etymology Dictionary". Etymonline.com. Archived from the original on 2011-06-06. Retrieved 2011-05-28.
9. ^ Watson, Lyall (2000-04-17). Jacobson's Organ: And the Remarkable Nature of Smell. W. W. Norton & Company. ISBN 978-0-393-24493-9.
10. ^ Dunlop, Jason A.; Penney, David (2012). Fossil Arachnids. Siri Scientific Press. p. 44\. ISBN 978-0-95677-954-0.
11. ^ 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.
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. ^ Feldhamer, George A. (2007-09-07). Mammalogy: Adaptation, Diversity, Ecology. JHU Press. ISBN 978-0-8018-8695-9.
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. ^ Dixson, Alan F. (2009). Sexual Selection and the Origins of Human Mating Systems. John OUP Oxford. p. 68\. ISBN 978-0-19156-973-9.
22. ^ 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.
23. ^ 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.
24. ^ 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.
25. ^ 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.
26. ^ Tyndale-Biscoe, C. Hugh; Renfree, Marilyn (1987-01-30). Reproductive Physiology of Marsupials. Cambridge University Press. ISBN 978-0-521-33792-2.
27. ^ Armati, Patricia J.; Dickman, Chris R.; Hume, Ian D. (2006-08-17). Marsupials. Cambridge University Press. ISBN 978-1-139-45742-2.
28. ^ Gadow, H. On the systematic position of Notoryctes typhlops. Proc. Zool. Soc. London 1892, 361–370 (1892).
29. ^ 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.
30. ^ Lutz, Dick (2005), Tuatara: A Living Fossil, Salem, Oregon: DIMI PRESS, ISBN 0-931625-43-2
31. ^ 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.
32. ^ Ruschenberger, William Samuel Waithman (1846). Elements of Herpetology, and of Ichthyology: Prepared for the Use of Schools and Colleges. Grigg & Elliot. pp. 129–145.
33. ^ "Penis | Description, Anatomy, & Physiology | Britannica". Encyclopædia Britannica. January 2024.
34. ^ 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.
35. ^ 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
36. ^ 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\. Bibcode:2014CBio...24.1006Y. doi:10.1016/j.cub.2014.03.022. hdl:2115/56857. ISSN 0960-9822. PMID 24746797.
37. ^ 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
38. ^ a b Yoshizawa K, Ferreira R.L., Kamimura Y & Lienhard C. "A Transgender Brazilian Cave Insect". The Winnower 3/9/2014
39. ^ Hollier J & Hollier A. (2020). "The retired taxonomist and the gynosome – the discovery of the female penis". Antenna 44(3): p. 122-125
40. ^ 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
41. ^ Rietstap, J. B. (1884). Armorial général; précédé d'un Dictionnaire des termes du blason. G. B. van Goor zonen. p. XXXI. "Vilené: se dit un animal qui a la marque du sexe d'un autre émail que le corps"

### General and cited references

[edit]

#### Horses

[edit]

* Walker, Donald F.; Vaughan, John T. (1 June 1980). Bovine and equine urogenital surgery. Lea & Febiger. ISBN 978-0-8121-0284-0. Retrieved 23 July 2013.
* "The Stallion: Breeding Soundness Examination & Reproductive Anatomy". University of Wisconsin-Madison. Archived from the original on 2007-07-16. Retrieved 7 July 2007.
* Munroe, Graham; Weese, Scott (15 March 2011). Equine Clinical Medicine, Surgery and Reproduction. Manson Publishing. ISBN 978-1-84076-608-0. Retrieved 18 February 2014.
* Budras, Klaus Dieter; Sack (1 March 2012). Anatomy of the Horse. Manson Publishing. ISBN 978-3-8426-8368-6. Retrieved 1 July 2013.
* England, Gary (15 April 2008). Fertility and Obstetrics in the Horse. John Wiley & Sons. ISBN 978-0-470-75041-4. Retrieved 18 February 2014.
* Equine Research (2004). Horse Conformation: Structure, Soundness, and Performance. Lyons Press. ISBN 978-1-59228-487-0. Archived from the original on 7 July 2014. Retrieved 23 July 2013.
* Evans, James Warren (15 February 1990). The Horse. W. H. Freeman. ISBN 978-0-7167-1811-6. Retrieved 23 July 2013.
* Hayes, M. Horace; Rossdale, Peter D. (March 1988). Veterinary Notes for Horse Owners: An Illustrated Manual of Horse Medicine and Surgery. Simon & Schuster. ISBN 978-0-671-76561-3. Retrieved 1 July 2013.
* McBane, Susan (2001). Modern Horse Breeding: A Guide for Owners. Globe Pequot Press. ISBN 978-1-58574-389-6. Archived from the original on 7 July 2014. Retrieved 18 February 2014.

#### Marsupials

[edit]

* Parker, Rick (13 January 2012). Equine Science (4 ed.). Cengage Learning. ISBN 978-1-111-13877-6. Retrieved 18 February 2014.
* Flannery, Tim (2008). Chasing Kangaroos: A Continent, a Scientist, and a Search for the World's Most Extraordinary Creature. Grove/Atlantic, Incorporated. pp. 60–. ISBN 9780802143716. Retrieved 5 May 2013.
* Hunsaker, Don II (2 December 2012). The Biology of Marsupials. Elsevier Science. ISBN 978-0-323-14620-3. Retrieved 18 February 2014.
* Jones, Menna E.; Dickman, Chris R.; Archer, Mike; Archer, Michael (2003). Predators With Pouches: The Biology of Carnivorous Marsupials. Csiro Publishing. ISBN 9780643066342. Retrieved 5 May 2013.
* King, Anna (2001). "Discoveries about Marsupial Reproduction". Iowa State University Biology Dept. Archived from the original on September 5, 2012. Retrieved 2012-11-22.
* Stonehouse, Bernard; Gilmore, Desmond (1977). The Biology of marsupials. University Park Press. ISBN 978-0-8391-0852-8. Retrieved 25 July 2013.
* Tyndale-Biscoe, C. Hugh (2005). Life of Marsupials. Csiro Publishing. ISBN 978-0-643-06257-3. Retrieved 18 February 2014.

#### Other animals

[edit]

* Austin, Colin Russell; Short, Roger Valentine (21 March 1985). Reproduction in Mammals: Volume 4, Reproductive Fitness. Cambridge University Press. ISBN 978-0-521-31984-3. Retrieved 22 July 2013.
* Bassert, Joanna M.; McCurnin, Dennis M. (1 April 2013). McCurnin's Clinical Textbook for Veterinary Technicians. Elsevier Health Sciences. ISBN 978-1-4557-2884-8. Retrieved 18 February 2014.
* Bates, Paul J. J.; Ratrimomanarivo, Fanja H.; Harrison, David L.; Goodman, Steven M. (December 2006). "A description of a new species of Pipistrellus (Chiroptera: Vespertilionidae) from Madagascar with a review of related Vespertilioninae from the island". Acta Chiropterologica. 8 (2): 299–324\. doi:10.3161/1733-5329(2006)8[299:ADOANS]2.0.CO;2. S2CID 85825521.
* Beck, Benjamin B.; Wemmer, Christen M. (1983). The Biology and management of an extinct species: Père David's deer. Noyes Publications. ISBN 978-0-8155-0938-7. Retrieved 5 July 2013.
* Burns, Eugene (1953). The sex life of wild animals: a North American study. Rinehart. Retrieved 23 July 2013.
* Carnaby, Trevor (22 January 2007). Beat About the Bush: Mammals. Jacana Media. ISBN 978-1-77009-240-2. Retrieved 19 July 2013.
* Brehm, Alfred Edmund (1895). Brehm's Life of Animals. Chicago: A. N. Marquis & Company. Retrieved 2013-11-08.
* Elbroch, Lawrence Mark; Kresky, Michael Raymond; Evans, Jonah Wy (7 April 2012). Field Guide to Animal Tracks and Scat of California. University of California Press. ISBN 978-0-520-95164-8. Retrieved 5 July 2013.
* Eltringham, Stewart Keith (1979). The ecology and conservation of large African mammals. Macmillan. ISBN 978-0-333-23580-5. Retrieved 20 July 2013.
* Estes, Richard (1998). The safari companion: a guide to watching African mammals, including hoofed mammals, carnivores, and primates. Chelsea Green Publishing. ISBN 978-1-890132-44-6.
* Frandson, Rowen D.; Wilke, W. Lee; Fails, Anna Dee (30 June 2009). Anatomy and Physiology of Farm Animals. John Wiley & Sons. ISBN 978-0-8138-1394-3. Retrieved 1 July 2013.
* Geist, Valerius (1993). Elk Country. T&N Children's Publishing. ISBN 978-1-55971-208-8. Retrieved 5 July 2013.
* Hayssen, Virginia Douglass; Tienhoven, Ari Van (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.
* Heptner, V. G.; Sludskii, A. A. (2002). Mammals of the Soviet Union. Vol. II, part 1b, Carnivores (Mustelidae and Procyonidae). Washington, D.C. : Smithsonian Institution Libraries and National Science Foundation. ISBN 978-90-04-08876-4. Retrieved 2013-11-08.
* Hoffmeister, Donald F. (2002). Mammals of Illinois. University of Illinois Press. ISBN 978-0-252-07083-9. Retrieved 22 July 2013.
* Hooper, E.T.; Musser, G.G. (1964). "The glans penis in Neotropical cricetines (Family Muridae) with comments on classification of muroid rodents". Miscellaneous Publications of the University of Michigan Museum of Zoology. 123: 1–57\. hdl:2027.42/56367.
* Horowitz, Barbara N.; Bowers, Kathryn (12 June 2012). Zoobiquity: What Animals Can Teach Us About Being Human. Doubleday Canada. ISBN 978-0-385-67061-6. Retrieved 25 July 2013.
* Horwich, Robert H. (June 1972). The ontogeny of social behavior in the gray squirrel (Sciurus carolinensis). P. Parey. ISBN 978-3-489-68036-9. Retrieved 23 July 2013.
* Jackson, Hartley H. (January 1961). Mammals of Wisconsin. Univ of Wisconsin Press. ISBN 978-0-299-02150-4. Retrieved 22 July 2013. `{{cite book}}`: ISBN / Date incompatibility (help)
* Journal of the Mammalogical Society of Japan. The Society. 1986. Retrieved 5 July 2013.
* Khanna, Dev Raj; Yadav, P. R. (1 January 2005). Biology Of Mammals. Discovery Publishing House. ISBN 978-81-7141-934-0. Retrieved 20 July 2013.
* Kingdon, Jonathan (January 1984). East African Mammals: An Atlas of Evolution in Africa. Vol. I. University of Chicago Press. ISBN 978-0-226-43718-7. Retrieved 22 July 2013.
* Kingdon, Jonathan (1984). East African Mammals: An Atlas of Evolution in Africa. University of Chicago Press. ISBN 9780226437187.
* König, Horst Erich; Liebich, Hans-Georg (2007). Veterinary Anatomy of Domestic Mammals: Textbook and Atlas. Schattauer Verlag. ISBN 978-3-7945-2485-3. Retrieved 23 July 2013.
* Kotpal, R. L. (2010). Modern Text Book Of Zoology Vertebrates. Rastogi Publications. ISBN 978-81-7133-891-7. Retrieved 23 July 2013.
* Krause, William J. (1 March 2008). An Atlas of Opossum Organogenesis. Universal-Publishers. ISBN 978-1-58112-969-4. Retrieved 20 July 2013.
* Linzey, Donald W. (28 December 2011). Vertebrate Biology. JHU Press. ISBN 978-1-4214-0040-2. Retrieved 20 July 2013.
* Lukefahr, Steven D.; Cheeke, Peter R.; Patton, Nephi M. (2013). Rabbit Production. CABI. ISBN 978-1-78064-012-9. Retrieved 20 July 2013.
* Natural History Bulletin of the Siam Society. 1975. Retrieved 5 July 2013.
* Percequillo, A.R.; Weksler, M.; Costa, L.P. (2011). "A new genus and species of rodent from the Brazilian Atlantic Forest (Rodentia: Cricetidae: Sigmodontinae: Oryzomyini), with comments on oryzomyine biogeography". Zoological Journal of the Linnean Society. 161 (2): 357–390\. doi:10.1111/j.1096-3642.2010.00643.x.
* Rose, Kenneth D.; Archibald, J. David (22 February 2005). The Rise of Placental Mammals: Origins and Relationships of the Major Extant Clades. JHU Press. ISBN 978-0-8018-8022-3. Retrieved 22 July 2013.
* Roze, Uldis (2009). The North American Porcupine. Cornell University Press. ISBN 978-0-8014-4646-7. Retrieved 25 July 2013.
* Sarkar, Amita (1 January 2003). Sexual Behaviour In Animals. Discovery Publishing House. ISBN 978-81-7141-746-9. Retrieved 20 July 2013.
* Schatten, Heide; Constantinescu, Gheorghe M. (21 March 2008). Comparative Reproductive Biology. John Wiley & Sons. ISBN 978-0-470-39025-2. Retrieved 23 July 2013.
* Small, Meredith F. (1993). Female Choices: Sexual Behavior of Female Primates. Cornell University Press. ISBN 978-0-8014-8305-9. Retrieved 23 July 2013.
* Skinner, J. D.; Chimimba, Christian T. (15 November 2005). The Mammals of the Southern African Sub-region. Cambridge University Press. ISBN 978-0-521-84418-5. Retrieved 19 July 2013.
* Staker, Lynda (2006). The Complete Guide to the Care of Macropods: A Comprehensive Guide to the Handrearing, Rehabilitation and Captive Management of Kangaroo Species. Lynda Staker. ISBN 978-0-9775751-0-7. Retrieved 19 July 2013.
* Strum, Shirley C.; Fedigan, Linda Marie (15 August 2000). Primate Encounters: Models of Science, Gender, and Society. University of Chicago Press. ISBN 978-0-226-77754-2. Retrieved 22 July 2013.
* Sturtz, Robin; Asprea, Lori (30 July 2012). Anatomy and Physiology for Veterinary Technicians and Nurses: A Clinical Approach. John Wiley & Sons. ISBN 978-1-118-40585-7. Retrieved 22 July 2013.
* Peter J Chenoweth; Steven Lorton (30 April 2014). Animal Andrology: Theories and Applications. CABI. ISBN 978-1-78064-316-8.
* Verts, B. J.; Carraway, Leslie N. (1998). Land Mammals of Oregon. University of California Press. p. 41\. ISBN 978-0-520-21199-5. Retrieved 20 July 2013.
* Voss, R.S.; Linzey, A.V. (1981). "Comparative gross morphology of male accessory glands among Neotropical Muridae (Mammalia: Rodentia) with comments on systematic implications". Miscellaneous Publications of the University of Michigan Museum of Zoology. 159: 1–41\. hdl:2027.42/56403.
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