[Viability at different stages of development and early embryogenesis of Drosophila virilis and D. littoralis and their hybrids].

The low percentage of larval hatching both in the initial lines and the hybrids of direct and back crosses was shown to be due to the low fertilizability of eggs. A study of early embryogenesis, up to the gastrulation, has shown that the F1 hybrids (female D. virilis x male D. littoralis) develop at a lesser rate than both the parental species. Some embryos of these latter attain the stage of blastoderm syncytium for 2 hrs whereas the hybrid embryos attain only the stage of polynuclear syncytium.