A comparative study of larval embryogenesis in the mosquito Culex fatigans Weidemann (Diptera : Culicidae) and the sheep-fly Lucilia sericata Meigen (Diptera : Calliphoridae) II. Casual interaction in embryonic development

Abstract

Results from cauterization and centrifugation experiments on the eggs of C, fatigans, and from cauterization, ligature, and centrifugation experiments on the eggs of L. sevicata give evidence that the mode and time of larval determination differ between the two species. All results for L. sericata indicate early larval determination with limited intragerm layer regulation, but lack of autonomy in segmentation in eggs ligated to the end of blastoderm formation. In C. fatigans, centrifugation of cleaving eggs resulted in frequent duplication of head structures. The results suggest the existence of an anterior centre responsible for determination of feeding brushes, ocelli, antennae, egg-breaker, and brain. Evidence for the existence of a posterior "activation" centre was inconclusive, In both C, fatigans and L. sevicata, pole cells are required for induction of the gonad sheath mesoderm. In C. fatigans the presumptive gonad sheath mesoderm is localized at gastrulation but in L. sevicata localization either does not exist or is not so precise. General confirmation of the presumptive fate maps constructed on the basis of descriptive studies (Davis 1967) was obtained.