1. The genitalia are paired in origin and appear to represent, in the male the coxites and telopodites of the ninth abdominal segment; in the female the telopodites of the eighth, and the coxites and telopodites of the ninth segments. 2. The testes and vasa deferentia, ovaries and oviducts, are paired and mesodermal in origin. 3. The efferent system, other than the testes and vasa deferentia, ovaries and oviducts, is unpaired and ectodermal in origin. 4. The gonopore is serially homologous in the male and female; but is posterior to the ninth segment in the former, and posterior to the eighth segment in the latter. 5. The ejaculatory duct and the median uterus are not strictly homologous, the ejaculatory duct being more comparable with the median accessory gland in the female. 6. There seems to be, in the females of the Insecta, a tendency for the gonopore to be shifted posteriorly.