Primary sexual organ of male animals
This article is about penises of animals in general. For the human organ, see
Human penis .
In many
animals , a penis (;
pl. : penises or penes ) is the main male
sexual organ used to
inseminate females (or
hermaphrodites ) during
copulation .
[1]
[2] Such organs occur in both
vertebrates and
invertebrates , but males do not bear a penis in every animal species.
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
The external genital organs appeared in the
Devonian , about 410 million years ago, when
tetrapods began to abandon the aquatic environment.
[6] In fact, it was necessary 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 ,
reptiles and
archosaurs (
crocodiles and
birds ).
Over time, birds have lost this organ, with the exception of
Paleognathae and
Anseriformes .
[7]
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 .
[8] 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.
Ejaculation is the ejecting of
semen from the penis and is usually accompanied by
orgasm . A series of muscular contractions delivers semen, containing male
gametes known as sperm cells or
spermatozoa , from the penis.
The last common ancestor of all living
amniotes (mammals, birds and reptiles) likely possessed a penis.
[9]
Vertebrates
Birds
A
mallard
pseudo-penis
[10]
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. 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
paleognathes (
tinamous and
ratites )
[11] and
Anatidae (ducks, geese and swans).
[12] 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.
[13] 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
As with any other bodily attribute, the length and girth of the penis can be highly variable between
mammals of different
species .
[14]
[15] In many mammals, the penis' flaccid size is smaller than its
erect size and is usually retracted into a
sheath .
Preputial glands are present in some sheaths. The penis bears
distal part of the
urethra in
placental mammals .
[8] 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:
[16]
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 .
[17]
[18] 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 .
[19]
Domestic cats have barbed penises, with about 120–150 one millimeter long
backwards-pointing spines .
[20]
Marsupials usually have bifurcated penises
[21] that are retracted into a preputial sheath in the male's
urogenital sinus when not erect.
[22]
Monotremes and
marsupial moles are the only mammals in which the penis is located inside the cloaca.
[23]
[24]
Fish and 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.
[25] Due to
evolutionary convergence , turtle and mammal penises have a similar structure.
[26]
In some fish, the
gonopodium ,
andropodium , and
claspers are intromittent organs (to introduce sperm into the female) developed from modified fins.
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 .
[27]
In 2010, entomologist Charles Linehard described
Neotrogla , a new genus of
barkflies . 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.
[28]
Heraldry
Pizzles are represented in
heraldry , where the adjective pizzled (or vilené
[29] ) indicates that part of an animate
charge 's anatomy, especially if coloured differently.
See also
References
Citations
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^
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External links
Look up
penis in Wiktionary, the free dictionary.
Wikimedia Commons has media related to
Penis .