Memoirs: Studies On the Development of the Genitalia and the Genital Ducts in Insects. I. Female of Orthoptera and Dermaptera
Authors: NEL R. I. 
Published: April 2021

1. The anterior ovipositor lobes (ventral valves) of Orthoptera are serially homologous with the lateral ovipositor lobes (dorsal valves) and represent gonocoxites from which no telopodites, corresponding to the inner valves, are differentiated.

2. The common oviduct originates as an unpaired ectodermal (hypodermal) invagination, in Blattella from the seventh intersternal membrane, in Locustana , Colemania, and Forficula between the seventh and eighth sterna, ending blindly, internally, between the ends of the mesodermal oviducts lying near the posterior margin of the seventh sternum.

3. In Blattella and Forficula the early condition is retained up to the adult stage; in Locustana and Colemania the common oviduct is secondarily extended posteriorly along the eighth sternum in the first instar, the gonopore coming to open in later instars, and in the adult on the inner reflexed surface of the eighth sternum.

4. Grooves are present in the early stages of Locustana, Colemania, and Blattella , between the bases of the ovipositor lobes on the eighth and ninth sterna, which become tubular anteriorly, giving rise each to an accessory genital invagination. The invagination from the eighth gives rise to the spermatheca in Locustana and Colemania; in Blattella it atrophies in late nymphal stages. The invagination from the ninth gives rise to the paired colleterial gland in Blattella; in Locustana and Colemania it develops slowly and gives rise to a vestigial accessory genital invagination. In Forficula no ovipositor lobes are present, and the invagination from the eighth arises practically intersegmentally between sterna 8 and 9. It also gives rise to the spermatheca in the adult. No accessory genital invagination is developed from the ninth sternum.

5. In Blattella four spermathecae are present. They originate as two pairs of separate hypodermal invaginations from the seventh intersternal membrane, morphologically posterior to the common oviduct invagination.

6. The primitive position of the single gonopore in the Orthoptera and Dermaptera is between sterna 7 and 8, its position in present-day Locustidae, Tettigoniidae, Gryllidae on the eighth sternum being secondary.

7. The spermathecal function was ancestrally associated with the accessory genital invagination from the eighth sternum in the Orthoptera. The four spermathecae of Blattella represent secondarily developed structures which do not correspond to the spermathecae of other Blattids, e.g. Periplaneta and other Orthoptera.

8. There is no evidence that part of the common oviduct is of mesodermal derivation or that it has a paired origin in the Orthoptera and in insects in general.

9. A hypothetical ancestral condition of the oviducal system and accessory organs is deduced for insects in general. The paired mesodermal oviducts opened separately within the seventh intersternal membrane, two gonopores being present. Accessory genital invaginations, possibly paired, were present on the eighth and ninth sterna at the bases of the gonopods, a spermathecal function probably being associated with the invagination(s) on the eighth sternum. Phylogenetic specialization consisted in an early acquisition of an ectodermal common oviduct and single gonopore between the seventh and eighth sterna, possibly polyphyletic, and a later extension posteriorly of the common oviduct and single gonopore on to the eighth and on to the ninth sterna, this posterior extension having definitely taken place polyphyletically.