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.

Synaptonemal complex complement of man in spreads of spermatocytes, with details of the sex chromosome pair.

Human pachytene chromosome pairs have been characterized electron microscopically in spread preparations on the basis of synaptonemal complex length, kinetochore position and attached nucleoli when present. The X and Y chromosomes can be followed by their filamentous axial cores from partial synapsis, through precocious disjuction and end-to-end attachment, to differentiation of a network in the sex chromosome pair.

A cinematographic study of the embryology ofDrosophila melanogaster.

In connection with studies on the effect of genetic abnormalities on development, a film was made of the normal development of theDrosophila embryo. Time-lapse motion technique was used, and this made it possible to make new observations on those phases of the development which involve large re-arrangements of the embryonic material, in particular on blastoderm formation, gastrulation and involution of the head. These new observations have been incorporated in an account of the complete development of the embryo up to the time of hatching.