Intromittent organ#Birds

{{see also|Penis#Invertebrates}}

Male cephalopods have a specialized arm, the hectocotylus, which is inserted into the female's mantle cavity to deliver a spermatophore during copulation. In some species, the hectocotylus breaks off inside the female's mantle cavity; in others, it can be used repeatedly to copulate with different females.{{cite book |editor1=José Iglesias |editor2=Lidia Fuentes |editor3=Roger Villanueva |title=Cephalopod Culture |date=2014 |publisher=Springer |page=29 |url=https://books.google.com/books?id=Ttg7BAAAQBAJ |access-date=23 August 2015|isbn=9789401786485 }}

In spiders, the intromittent organs are the male pedipalps, even though these are not primarily sexual organs, but serve as indirect mating organs; in the male the pedipalps have hollow, clubbed tips, often of complex internal anatomy. The sexually mature male typically deposits semen from the palpal bulb onto a specially woven silken mat, then sucks the emission into his pedipalps. In mating, he inserts the openings of the pedipalps in turn into the epigyne, the female external genital structure.{{citation needed|date=September 2015}}

In Solifugae, sperm transfer is also indirect; the male deposits a spermatophore on the ground, picks it up in his chelicerae, then inserts it into the female's genital opening.

In Opiliones (harvestmen), males have a structure called a penis, which is not present in other arachnids.

In most millipedes, sperm transfer is performed by one or two pair of modified legs called gonopods, which are often on the seventh body segment. During mating, a male bends his body to collect a spermatophore from the genital pore of his third segment, and inserts it into the female's body. Gonopods vary greatly among millipedes, and are often used to identify species.{{cite web|title=Reproductive behaviour in invertebrates|url=http://www.britannica.com/topic/reproductive-behaviour-zoology/Reproductive-behaviour-in-invertebrates#ref497574|website=Encyclopædia Britannica|access-date=23 August 2015}}

Male insects possess an aedeagus, whose function is directly analogous to that of the vertebrate penis. Some insects also have claspers. Male moths have an additional organ called the juxta, which supports the aedeagus. These however are generalisations, and insect genitalia vary enormously in anatomy and in application. For example, some insects, most notoriously the Cimicidae and some Strepsiptera, practise traumatic insemination, in which the intromittent organ pierces the abdominal wall and the semen is deposited into the hemocoel.{{cite book|first1=R.F. |last1=Chapman |first2=Angela E. |last2=Douglas |year=2013 |title=The Insects: Structure and Function|page=304|publisher=Cambridge University Press |url=https://books.google.com/books?id=NXJEi8fo7CkC&pg=PA304 |access-date=23 August 2015|isbn=9780521113892 }}

File:Black Molly 3 Male.jpg of a black molly (Poecilia sphenops).]]

In male members of Chondrichthyes (sharks and rays), as well as now-extinct placoderms, the pelvic fins bear specialized claspers. During copulation, one clasper is inserted into the female's cloaca, and sperm is flushed by the male's body through a groove into the female.{{cite web|title=Urogenital Anatomy of the Dogfish Shark|url=http://www.pc.maricopa.edu/Biology/ppepe/BIO145/lab04_5.html|website=Maricopa Community Colleges|access-date=23 August 2015}}

Members of Poeciliidae are small fishes that give birth to live young. In males, the anal fin is shaped into a grooved, rod-shaped organ called a gonopodium used to deliver sperm to females.{{cite book|last1=Scott|first1=Thomas|title=ABC Biologie|page=554|url=https://books.google.com/books?id=LorrYj5pkKYC&q=In+males,+the+anal+fin+is+shaped+into+a+grooved,+rod-shaped+organ&pg=PA554|access-date=23 August 2015|isbn=9783110106619|year=1996|publisher=Walter de Gruyter }}

In lizards and snakes, males possess paired hemipenes, each of which is usually grooved to allow sperm transport and spiny or rough at the tip to allow firm attachment to the female.{{cite web|title=Hemipenes of snakes and lizards|url=http://cumuseum.colorado.edu/exhibits/objects/hemipenes-snakes-and-lizards|website=University of Colorado Boulder Museum of Natural History|access-date=23 August 2015|url-status=dead|archive-url=https://web.archive.org/web/20150826033020/http://cumuseum.colorado.edu/exhibits/objects/hemipenes-snakes-and-lizards|archive-date=26 August 2015|df=dmy-all}} To become erect, a hemipenis is evaginated (turned inside out) through muscle action and engorgement with blood. Only one is inserted into the female's cloaca at a time.{{cite book|title=Annual Report of the Board of Regents of the Smithsonian Institution|date=1900|page=700|url=https://books.google.com/books?id=Cbk6AQAAMAAJ&q=hemipenis+is+evaginated&pg=PA700|access-date=23 August 2015}} In reptiles, the phallus has an open sulcus instead of a closed urethral tube.Gredler, Marissa L., et al. "[https://www.karger.com/Article/FullText/365771 Evolution of external genitalia: insights from reptilian development]." Sexual Development 8.5 (2014): 311-326.

In some turtles, crocodiles, some birds, and in all mammals, males possess a penis centered along the midline of the body. During copulation, it becomes erect due to engorgement with blood or lymph, though in many animals it also contains a stiff or even bony support structure. When not in use, its soft penile tissue is usually flaccid, and depending on the species, may be retracted into the body. The anatomy of the penis varies widely according to species. However, the penis evolved only once in the evolutionary history of amniotes.{{Cite journal|last=Brennan|first=Patricia L.R.|date=January 2016|title=Evolution: One Penis After All |journal=Current Biology |volume=26|issue=1|pages=R29–R31|doi=10.1016/j.cub.2015.11.024|pmid=26766229|issn=0960-9822|doi-access=free|bibcode=2016CBio...26..R29B }} In male caecilians, the intromittent organ is called the phallodeum.{{cite book|author=Barrie G M Jamieson|title=Reproductive Biology and Phylogeny of Gymnophiona: Caecilians|url=https://books.google.com/books?id=a0hZDwAAQBAJ |date=5 January 2006|publisher=CRC Press|isbn=978-1-4822-8014-2}}{{cite book|author1=William E. Duellman|author2=Linda Trueb|author-link2=Linda Trueb|title=Biology of Amphibians|url=https://books.google.com/books?id=CzxVvKmrtIgC |date=February 1994|publisher=JHU Press|isbn=978-0-8018-4780-6}}

{{main article|Mammalian penis}}

File:Armand de Montlezun Baculum Pyrénées.jpg of a dog (Canis lupus familiaris).]]

All male mammals have a penis.{{cite book |author=Libbie Henrietta Hyman |url=https://books.google.com/books?id=VKlWjdOkiMwC&pg=PA583 |title=Hyman's Comparative Vertebrate Anatomy |date=15 September 1992 |publisher=University of Chicago Press |isbn=978-0-226-87013-7 |pages=583–}}{{Cite book |last=Chenoweth |first=Peter J. |url=https://www.google.com/books/edition/Manual_of_Animal_Andrology/3JtcEAAAQBAJ?hl=en&gbpv=1&dq=ejaculation+penis+copulation+mammals+birds&pg=PA16&printsec=frontcover |title=Manual of Animal Andrology |last2=Lorton |first2=Steven P. |date=2022-02-03 |publisher=CABI |isbn=978-1-78924-350-5 |language=en}} Eulipotyphlans, bats, rodents, carnivorans, and most primates (but not humans) have a bone called the baculum or os penis that permanently stiffens the penis. During copulation, blood engorges the already-stiff penis resulting in a full erection.{{cite web|title=Baculum (penile bone) in mammals|url=http://www.mapoflife.org/topics/topic_203_Baculum-(penile-bone)-in-mammals/|website=Map of Life|access-date=23 August 2015}}

Monotreme penes are variously unusual; the platypus has a penis with a two-lobed (bifid) tip though the whole shaft is inserted in mating, possibly to engage both of the uterine branches, but the echidna's penis actually has four heads, only two of which function at a time.{{cite book|last1=Grant|first1=Tom|title=The Platypus: A Unique Mammal|date=1995|publisher=UNSW Press|page=36|url=https://books.google.com/books?id=FASJWgDhxIsC&q=Monotreme+penis&pg=PT55|access-date=23 August 2015|isbn=9780868401430}}{{Cite journal | doi=10.1086/522847 |doi-access=free | pmid=18171162|title = One-Sided Ejaculation of Echidna Sperm Bundles| journal=The American Naturalist| volume=170| issue=6| pages=E162–E164|year = 2007|last1 = Johnston|first1 = S.D.| last2=Smith| first2=B.| last3=Pyne| first3=M.| last4=Stenzel| first4=D.| last5=Holt| first5=W.V.}} Both monotremes and marsupial moles are the only mammals with internal penises, located on the cloacal wall instead of outside of it as in other mammals.Gadow, H. On the systematic position of Notoryctes typhlops. Proc. Zool. Soc. London 1892, 361–370 (1892).{{cite journal |last1=Riedelsheimer |first1=B. |last2=Unterberger |first2=Pia |last3=Künzle |first3=H. |last4=Welsch |first4=U. |title=Histological study of the cloacal region and associated structures in the hedgehog tenrec Echinops telfairi |journal=Mammalian Biology |date=November 2007 |volume=72 |issue=6 |pages=330–341 |doi=10.1016/j.mambio.2006.10.012 |bibcode=2007MamBi..72..330R |url=https://www.researchgate.net/publication/248908391}}

Most marsupial penises are variously forked or split into two in such ways that they resemble hemipenes;{{cite book|author1=Hugh Tyndale-Biscoe|author2=Marilyn Renfree|title=Reproductive Physiology of Marsupials|url=https://books.google.com/books?id=HpjovN0vXW4C|date=30 January 1987|publisher=Cambridge University Press|isbn=978-0-521-33792-2}}{{cite book|author=C. Hugh Tyndale-Biscoe|title=Life of Marsupials|url=https://books.google.com/books?id=gDFeNMhJlPUC|year=2005|publisher=Csiro Publishing|isbn=978-0-643-09199-3}} in different marsupial species their forms are characteristic enough to be taxonomically important.{{cite book|author1=Menna Jones|author2=Chris R. Dickman|author3=Mike Archer|author4=Michael Archer|title=Predators with Pouches: The Biology of Carnivorous Marsupials|url=https://books.google.com/books?id=3YQSDiWHfD0C|year=2003|publisher=Csiro Publishing|isbn=978-0-643-06634-2}}{{cite book|last1=Sadleir|first1=Richard|title=The Reproduction of Vertebrates|date=1973|isbn=978-0-12-614250-1|page=120|publisher=Elsevier |url=https://books.google.com/books?id=PVP-wS9UXwoC&q=penis|access-date=23 August 2015}}

{{main article|Penis#Birds}}

Although birds reproduce through internal fertilization, 97% of males completely lack a functional intromittent organ.{{cite book|last=Montgomerie|first=R.|title=The Evolution of Primary Sexual Characters in Animals|year=2010|publisher=Oxford University Press|location=New York|pages=453–470|editor=J. L. Leonard and A. Córdoba-Aguilar|chapter=Sexual Conflict and the Intromittent Organs of Male Birds|isbn=9780199886753|chapter-url=https://books.google.com/books?id=SknTBgAAQBAJ&q=%22Sexual+Conflict+and+the+Intromittent+Organs+of+Male+Birds%22&pg=PT980}} For the 3% of birds with an intromittent organ, copulation occurs through brief insertion of the male organ into the vagina before ejaculation.{{cite journal|last=Briskie|first=J. V.|author2=R. Montgomerie |title=Sexual Selection and the Intromittent Organ of Birds|journal=Journal of Avian Biology|year=1997|volume=28|issue=1|pages=73–86 |doi=10.2307/3677097|jstor=3677097}} Alternatively, for the vast majority of birds—a group comprising nearly 10,000 species{{cite journal|last=Herrera|first=A. M.|author2=S. G. Shuster |author3=C. L. Perriton |author4= M. J. Cohn |title=Developmental Basis of Phallus Reduction During Bird Evolution|journal=Current Biology |year=2013|volume=23|pages=1065–1074|doi=10.1016/j.cub.2013.04.062|pmid=23746636|issue=12|doi-access=free|bibcode=2013CBio...23.1065H }}—sperm transfer occurs by cloacal contact between the male and female, in a maneuver known as the "cloacal kiss". Birds are one of the only groups which reproduce through internal fertilization but have repeatedly lost the intromittent organ.{{Cite journal|last1=Briskie|first1=James V.|last2=Montgomerie|first2=Robert|date=1997|title=Sexual Selection and the Intromittent Organ of Birds|journal=Journal of Avian Biology|volume=28|issue=1|pages=73–86|doi=10.2307/3677097|jstor=3677097}}

Male ostriches have a conical shaped penis that is wider at the base.{{cite journal |last1=Brennan |first1=P.L.R. |last2=Prum |first2=R.O. |last3=Hayssen |first3=Virginia |title=The erection mechanism of the ratite penis |journal=Journal of Zoology |date=February 2012 |volume=286 |issue=2 |pages=140–144 |doi=10.1111/j.1469-7998.2011.00858.x |url=http://prumlab.yale.edu/sites/default/files/brennan_prum_2011.pdf }}

A functional intromittent organ is known to be present in most species of Paleognathae and Anseriformes. The Anseriformes (waterfowl) are a particularly interesting group to study given the high variability in intromittent organ morphology. Waterfowl intromittent organs range greatly in length, are often characterized by surface elaborations (both spines and grooves), and at times spiral counter-clockwise.{{cite journal|last=Birkhead|first=P. L. R.|author2=R. O. Prum |author3=K. G. McCracken |author4=M. D. Sorenson |author5=R. E. Wilson |author6= T. R. Birkhead |title=Coevolution of Male and Female Genital Morphology in Waterfowl|journal=PLOS ONE|year=2007|volume=2|pages=e418|bibcode=2007PLoSO...2..418B|doi=10.1371/journal.pone.0000418|pmid=17476339|issue=5|pmc=1855079|editor1-last=Pizzari|editor1-first=Tom|doi-access=free}} Male ducks have a penis that is coiled along the ventral wall of the cloaca when flaccid and which may have an elaborate spiral shape when erect. Waterfowl intromittent organ variation is most likely due to an intersexual arms race resulting from a mating system in which forced extra-pair copulations are frequent.{{cite journal|last=Adler|first=M.|title=Sexual Conflict in Waterfowl: Why do Females Resist Extrapair Copulations?|journal=Behavioral Ecology|year=2010|volume=21|pages=182–192|doi=10.1093/beheco/arp160|doi-access=free}}

• {{cite book |title= Vertebrates: Comparative Anatomy, Function, Evolution |pages= 567–570 |last= Kardong |first= Kenneth V. |publisher= Wm. C. Brown Publishers |location = Dubuque, Iowa |year= 1995 |isbn= 978-0-06-921991-9 }}

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Category:Animal male reproductive system

Category:Comparative anatomy

Category:Sexual anatomy