A
penis (plural
penises or
penes ) is the primary
sexual organ that
male and
hermaphrodite animals use to
inseminate sexually receptive mates (usually females and hermaphrodites respectively) 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.