The ultrastructure of oogenesis in Culex theileri

The 12-36 h post blood meal (PBM) oocyte in C. theileri is characterized by a dramatic increase in the quantity of protein with concomitant changes in the adjacent follicular epithelium. The cytoplasm shows a preponderance of mitochondria and rough endoplasmic reticulum in proportion to free ribosomes. Numerous Golgi complexes, which bud off secretory granules, are also found scattered in the cytoplasm. These changes are concerned with the deposition of the vitelline membrane and by 36 h PBM, a continuous vitelline membrane is formed at the follicle cell-oocyte interface. Vitellogenesis appears to be completed by 48 h PBM and the final maturation stages are concerned solely with deposition of the chorionic membrane. In C. theileri the chorionic membrane seems to be synthesized in a similar manner to the vitelline membrane; namely from the aggregation of secretory droplets and only proceeds once the vitelline membrane formation is completed. The chorionic membrane is made up of an endochorion and an exochorion. Although the structural complexity of the follicular epithelium is maintained at 48 h PBM, its appearance at 60 h PBM is indicative of degenerative changes. By 60 h PBM synthesis of both the vitelline and chorionic membranes has been completed and vitellogenesis has ceased. This stage then represents the complete maturation of the ovum in C. theileri

A micro-environmental study of the effect of temperature on the sex ratios of the loggerhead turtle, Caretta caretta, from Tongaland, Natal

Sex determination in C. caretta is, under natural conditions, dependent on incubation temperature. In general, below 27°C all hatchlings are male while above 29,3°C 80% or more are females. The sex ratios of the nests were also dependent on the time of season which is directly related to temperature. Metabolic heating of the nest was evident only towards the end of the critical period i.e. post-sexual differentiation. There was no correlation between sex ratios and the physical characteristics of the beach. The implications of temperature sex determination on the limitation of geographical populations are also discussed

Book Reviews

Book Review 1Book Title: Reproductive Energetics in MammalsBook Authors: A.S.I. Loudon & P.A. Racey (Eds.)Zoological Society of London Symposia 57, 1987 Clarendon. Press, Oxford. 371 pp.Book Review 2Book Title: Classification of Southern African MammalsBook Authors: J.A.J. Meester, I.L. Rautenbach, N.J. Dippenaar & C.M. BakerTransvaal Museum Monograph No.5. 359 pp.Book Review 3Book Title: Pesticide impact on stream fauna with special reference to macroinvertebratesBook Author: R.C. Muirhead-ThomsonCambridge University Press, 1987. 275 pp.Book Review 4Book Title: Evolution of sex determining mechanismsBook Author: James J. BullBenjamin-Cummings Publ. Company / Addison-Wesley Publishing Group, JohannesburgBook Review 5Book Title: The evolutionary ecology of ant-plant mutualismsBook Author: Andrew J. BeattieCambridge University Press 182 pp.Book Review 6Book Title: The Ecology of SexBook Authors: P.J. Greenwood & J. Adams Edward Arnold, London, 1987. 74 pagesBook Review 7Book Title: The Dinosaur Heresies - a revolutionary view of dinosaursBook Author: Robert BakkerPublished by Longman Scientific and Technical, 1987Book Review 8Book Title: Molecular Biology of the GeneBook Authors: Watson, Hopkins, Roberts, Steitz & WeinerVolumes I and II (Fourth Edition) (Benjamin/Cummings. Menlo Park); Addison-Wesley Publishing Group. Johannesburg 1163 pp.Book Review 9Book Title: Evolutionary BiologyBook Author: Eli C. MinkoffAddison-Wesley Publishing Company, Massachussets, 1983. 627pp.Book Review 10Book Title: An ecosystem approach to aquatic ecology. Mirror Lake and its environmentBook Author: Gene E. Likens (Ed.)Springer-Ver1ag, New York. xiv - 516 pages; 197 figuresBook Review 11Book Title: The Physiological Ecology of SeaweedsBook Authors: C.S. Lobban, P.J. Harrison & M.J. Duncan Cambridge University press, Cambridge, 1985. 242 pagesBook Review 12Book Title: Principles of ecologyBook Authors: R.J.Putman & S.D. WrattenCroom Helm, London, 1984. 388 pages