A study on Penis

Penis (plural penises or penes) is a general term for the organs with which male and hermaphrodite animals introduce sperm into receptive females 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 penes in the various species are not necessarily homologous. For example, the penis of a mammal is at most analogous to the penis of a male insect or barnacle.
The term penis applies to many reproductive intromittent organs, but not to all; for example the intromittent organ of most cephalopoda is the hectocotylus, a specialised arm, and male spiders use their pedipalps.
In most species of animals in which there is an organ that might reasonably be described as a penis, it has no major function other than intromission, or at least conveying the sperm to the female, but in the placental mammals the penis bears the distal part of the urethra, which discharges both urine during urination and semen during copulation as the occasion requires. The Blue Whale has the largest penis of any organism on the planet, typically measuring 8-10 feet.
Contents [hide]
1 In different animals
1.1 Vertebrates
1.1.1 Mammals
1.1.2 Other vertebrates
1.2 Invertebrates
2 Etymology
3 See also
4 References
5 External links
In different animals

Vertebrates
Mammals
Further information: Sexual reproduction in male mammals
For the male human sexual organ, see Human penis.

Penis of an Asian elephant.
As with any other bodily attribute, the length and girth of the penis can be highly variable between individuals of the same species. In many animals, especially mammals, the size of a flaccid penis is smaller than its erect size.
A bone called the baculum or os penis is present in most mammals but absent in humans and horses.
In mammals the penis is divided into three parts:[1]
Roots (crura): these begin at the caudal