Aedeagus

aedeagi) is a reproductive organ of male arthropods through which they secrete sperm from the testes during copulation with a female.

The term is derived from Ancient Greek αἰδοῖα (aidoia) 'private parts' and ἀγός (agos) 'leader'.

In some species the phallotheca contains a space, called the endosoma (internal holding pouch), into which the tip end of the aedeagus may be withdrawn (retracted).

In addition to the spermatophores, in some species the aedeagus also discharges a spermatophylax, a ball of nutritious secretions, as a nuptial gift to aid the female in producing offspring.

In males of most species of Lepidoptera, the aedeagus has a sheath which is supported by an organ called the juxta, which is located between the aforementioned valvae.