SummaryTheadultLeucinodes orbonalishas a median testicular mass from the posterior side of which a pair of vasa deferentia arises. Each vas deferens swells to form a seminal vesicle which continues behind into the long coiled paired ejaculatory duct into which also opens an accessory gland. The two paired ducts join to form the unpaired ejaculatory duct. The tubular aedeagus has a leafy valve on each side. The genitalia are covered above by a broad tegumen bearing a spherical uncus at its apex. The vinculum is a narrow plate below.The aedeagus and valves develop from the bifurcation of a pair of genital rudiments arising on the ninth sternum of the larva and hanging into the primary genital invagination formed on the ninth sternal region. The tegumen and uncus arise from the ninth and tenth terga respectively and the vinculum from the ninth sternum.The paired ejaculatory ducts arise as paired rudiments from the apex of the primary genital invagination. The accessory glands originate from the longitudinal splitting of the anterior ends of these rudiments. True vasa deferentia are formed from the testicular covering and join the paired ejaculatory ducts in the region of the eighth segment. The unpaired ejaculatory duct develops by the fusion of the aedeagus lobes and from the ectodermal invagination between them. The paired testes fuse with each other to form a median mass.