Morphogenesis in the embryo ofDrosophila melanogaster -germ band extension in the maternal-effect lethalmat(3)6.

In the maternal-effect embryonic lethalmat(3)6, although cell formation occurs only at the poles, posterior blastoderm cells give rise to a posterior midgut rudiment (PMG) that undergoes extension movements similar to those in normal embryos (Rice and Garen 1975). Inmat(3)6 embryos, PMG cells retain cytoplasmic continuity with the yolk sac during early extension, and a microfilament system is present in the yolk sac beneath and anterior to the PMG. This correspondence between normal and mutant embryos in what we have postulated to be essential structural components of the morphogenetic system (Rickoll and Counce 1980) supports our interpretation that the yolk sac has a causal role in early germ band extension.

Morphogenesis in the embryo ofDrosophila melanogaster - Germ band extension.

Changes at the ultrastructural level during germ band extension in the embryo ofDrosophila melanogaster are described. Cytoplasmic connections between cells and the yolk sac are present during initial cellular movements. At this time, a continuous system of microfilaments is present adjacent to the membranes in the connections and at the periphery of the yolk sac.

Synaptonemal complex karyotyping in Melanoplus differentialis.

The chromosomal axes of the spermatocytes of the grasshopper Melanoplus differentialis have been studied with a modification of the microspreading procedure used previously. The whole complement of synaptonemal complexes (SCs) and the axis of the X chromosome have been described and measured. The relative length of each SC is characteristic and constant and permits the construction of an idiogram.