Much debate continues regarding the evolutionary origin of hemipenes and its relationship to the intromittent organs of other species. However, embryonic and molecular research is beginning to shed light on the origin of the hemipenis.
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Male cartilaginous fishes (sharks and rays), as well as the males of some live-bearing ray finned fishes, have fins that have been modified to function as intromittent organs, reproductive appendages which allow internal fertilization. In ray finned fish they are called gonopodia or andropodia, and in cartilaginous fish they are called claspers. Gonopodia are found on the males of some species in the Anablepidae and Poeciliidae families. They are anal fins that have been modified to function as movable intromittent organs and are used to impregnate females with milt during mating.
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The spined pygmy shark may also be referred to as the dwarf shark or the bigeye dwarf shark. Based on similarities in their claspers (male intromittent organs), the closest relative of the spined pygmy shark and the related S. aliae is thought to be the pygmy shark (Euprotomicrus bispinatus).
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Female polymorphism could in fact be a result of evolution due to sexual conflict. Male spiders Harpactea sadistica perform extra-genitalic traumatic insemination with their needle- like intromittent organs that puncture the female's wall, resulting in direct insemination. Males also puncture females with their cheliceral fangs during courtship. Females have atrophied spermathecae (sperm-storage organs).
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Sharks practice internal fertilization. The posterior part of a male shark's pelvic fins are modified into a pair of intromittent organs called claspers, analogous to a mammalian penis, of which one is used to deliver sperm into the female. Mating has rarely been observed in sharks. The smaller catsharks often mate with the male curling around the female.
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The female now had to fetch the spermatophore from the male venter. This created an adaptive pressure to create storage structures for the spermatophore and attachment structures for the female genitalia. Tarsophlebiidae probably represent this state of evolution. The development of liquid sperm and intromittent organs for copulation apparently evolved three times in parallel in the three extant suborders.
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An intromittent organ is a general term for an external organ of a male organism that is specialized to deliver sperm during copulation. Intromittent organs are found most often in terrestrial species, as most non-mammalian aquatic species fertilize their eggs externally, although there are exceptions. For many species in the animal kingdom, the male intromittent organ is a hallmark characteristic of internal fertilization.
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Male ostriches have a conical shaped penis that is wider at the base. 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.
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He slowly walks in circles around the female with stiffened legs. The female will either submit, and allow the male to mount her, or retreat to her burrow. Males do not have a penis; they have rudimentary hemipenes; meaning that intromittent organs are used to deliver sperm to the female during copulation. They reproduce by the male lifting the tail of the female and placing his vent over hers.
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Newborns measure in length. Males reach sexual maturity at a length of , and females at a length of . A study of brown lanternsharks in Suruga Bay by Yano and Tanaka (1989) found a 23% prevalence of hermaphroditism within the population. Of the 16 hermaphrodites examined, 15 were functional females (and some were pregnant) that also possessed well- developed claspers (male intromittent organs), while one was a functional male with ovarian tissue in the left testis.
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In male species with intromittent organs, during copulation, a male inserts his reproductive organ into that of a female's so as to inseminate her with his genetic material. Through the development of mechanisms that either prematurely inhibit copulation or act following male insemination, females are able to prevent undesirable males from successfully fertilizing their eggs. Thus, not every copulatory event is successful – there are many factors that combine to determine whether or not an offspring is created.
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They are the posterior part of the pelvic fins that have also been modified to function as intromittent organs, and are used to channel semen into the female's cloaca during copulation. The act of mating in sharks usually includes raising one of the claspers to allow water into a siphon through a specific orifice. The clasper is then inserted into the cloaca, where it opens like an umbrella to anchor its position. The siphon then begins to contract expelling water and sperm.
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An everted hemipenis of a North American rattlesnake (Crotalus adamanteus). Common House Geckos, mating, ventral view with hemipenis inserted in the cloaca A hemipenis (plural hemipenes) is one of a pair of intromittent organs of male squamates (snakes, lizards and worm lizards). Hemipenes are usually held inverted within the body, and are everted for reproduction via erectile tissue, much like that in the human penis. They come in a variety of shapes, depending on species, with ornamentation, such as spines or hooks.
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The hemipenis is the intromittent organ of squamata, which is the second largest order of vertebrates with over 9000 species distributed around the world. They differ from the intromittent organs of most other amniotes such as mammals, archosaurs and turtles that have a single genital tubercle, as squamates have the paired genitalia remaining separate. Squamate hemipenes also develop from a different cell origin, originating from the same embryonic cells that produce the limbs, whereas mammalian penises arise from the embryonic cells that develop the tail.
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The hammerhead sharks exhibit a viviparous mode of reproduction with females giving birth to live young. Like other sharks, fertilization is internal, with the male transferring sperm to the female through one of two intromittent organs called claspers. The developing embryos are at first sustained by a yolk sac. When the supply of yolk is exhausted, the depleted yolk sac transforms into a structure analogous to a mammalian placenta (called a "yolk sac placenta" or "pseudoplacenta"), through which the mother delivers sustenance until birth.
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A male Crotalus atrox with a pair of intromittent organs called hemipenes, used for reproduction Rattlesnakes, including C. atrox, are viviparous. Gestation lasts six or seven months, and broods average about a dozen young. However, the young stay with the mother for only a few hours before they set off on their own to hunt and find cover, so that the mortality rate is very high. Mating occurs in the fall, and the females give birth to as many as 25 young, which may be as long as .
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A penis (plural penises or penes ) is the primary sexual organ that male animals use to inseminate females (or hermaphrodites) during copulation. Such organs occur in many animals, both vertebrate and invertebrate, but males do not bear a penis in every animal species, and in those species in which the male does bear a so-called penis, the penises in the various species are not necessarily homologous. 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.
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Although it cannot be genetically determined what dictates minimum and maximum post-puberty sizes of Macropodia Rostrata, scientists believe it is the result of varied ecological histories. Interestingly, it was expected that the males of the species Macropodia Rostrata would show modification of the gential papillae and the first intromittent organs coinciding with the molt of puberty, however it was observed that the size of carapace length and gential papillae did not correlate. For male Macropodia Rostrata, the largest pre puberty carapace lengths are 18mm, while the mean is generally 16.4mm. Male macropodia Rostrata can reach a maximum post-puberty carapace length of 23mm.
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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 his semen 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. 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.
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