Endofallus

Endofallus (from other Greek: ἔνδον “inside” and φαλλός “male genital organ”), sometimes also an internal sac or vesic — an internal membranous part of the penis that turns out when copulating in insects .

At rest in insects , only the bases of the endofallus walls protrude outward, which are attached to the edges of the dorsal opening of the copulatory organ. From the inside, the ejaculatory canal approaches the gonopore (opening) on ​​the apical part of the endofallus. In an erection state, the endofallus is filled with hemolymph , as a result of which it turns out. At the same time, the ejaculatory canal is stretched and placed in the cavity of the inverted endofallus. During copulation, endofallus is fixed in the copious bag of the female by microtrichia and sclerites located on its walls.

The shape of the inverted and swollen endofallus is constant and, as a rule, specific for each species. Isolated and prepared endofalli are often used by entomologists in determining species, most often coleoptera , from various families, as well as in studying the systematics and phylogeny of various groups of insects.