Aedeagus

The aedeagus is the male intromittent organ of many insects and other invertebrates. It is used to transfer sperm to the female during copulation and is typically housed within the abdomen, being everted only during mating in many species.

Anatomically, the aedeagus often consists of a basal portion and a median lobe or shaft that contains the phallus or vesica. In many taxa, the vesica can be inflated or extended during copulation to deliver sperm. Additional structures, such as parameres or lobes, may assist in grasping or positioning the organ during mating. Because of its high structural diversity, the aedeagus shows extensive species-specific variation.

Significance: The shape and internal configuration of the aedeagus are widely used in insect taxonomy and phylogenetic studies, particularly for distinguishing closely related species. Its evolution is influenced by sexual selection and co-evolution with female genitalia.

Development and variation: The organ develops during metamorphosis from tissues of the terminal abdomen, and the precise morphology varies widely among groups, providing a key diagnostic feature for systematists.