The main part of the thesis is a description of the reproductive system of the opisthobranch molluscs Philine aperta, Acteonia cocksii, Alderia modesta, Archidoris britannica and Idulia fraRilis. Reference is made to ten other genera which differ from these only in detail. In all, the initial part of the reproductive duct, which corresponds to the gonadial and renal sections of the prosobranchs, shows uniformity of structure and histology and part functions as a vesicula seminalis. The pallial region of the reproductive duct of a prosobranch contains oviducal and vaginal channels, but with the development of hermaphroditism the opisthobranchs require an additional male pathway for outgoing sperm. In the tectibranchs (except the Pleurobranchidae) incomplete separation of oviducal, vaginal and seminal channels is achieved by means of septa; in all others three separate ducts are present, the arrangement of which conforms to one of three plans represented by the Sacoglossa, the dorids and Idulia respectively. All three types may be derived, independently, from tectibranch-like ancestors. The development of a penial sheath in the opisthobranchs may be correlated either with the loss of mantle cavity or with the retention of the penis at the anterior end of the body remote from this. Two vesicles are associated with the vaginal pathway -a receptaculum and a bursa copulatrix. The functions of these vesicles are compared with those of the corresponding structures in the prosobranchs. Since male and female gametes are present simultaneously in the reproductive ducts the mechanism by which self-fertilization may be prevented is discussed. The type of spawn and its formation are compared with those of prosobranchs.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:519794 |
| Date | January 1952 |
| Creators | Lloyd, H. M. |
| Publisher | Birkbeck (University of London) |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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