Genitalia in male and female of any Butterfly species are adapted to fit each other like a lock (female) and key (male). In males, the ninth abdominal segment is divided into a dorsal 'tegumen' and ventral 'vinculum'. They form a ring-like structure for the attachment of genital parts and a pair of lateral clasping organs (claspers or 'harpe').
The male has a median tubular organ (called the aedeagus) which is extended through an eversible sheath (or 'vesica') to inseminate the female. The males have paired sperm ducts in all Lepidopterans; however, the paired testes are separate in basal taxa and fused in advanced forms.
The males of many species of Papilionoidea are furnished with secondary sexual characteristics. These consist of scent-producing organs, brushes, and brands or pouches of specialised scales. These presumably meet the function of convincing the female that she is mating with a male of the correct species.
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