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Abstract:
Drosophila melanogaster embryos at the cellular blastoderm stage were irradiated with a uv laser microbeam (257 nm, 7 erg) of 20-μm diameter. Depending on the site of irradiation, up to 90% of the resulting first-instar larvae showed defects in the integument. The location of the defects within the cuticular pattern corresponded closely to the site of irradiation. The data indicate that the anlagen for the left and right parts of the larval epidermis are separated ventrally and each occupies an area extending from 20 to 60% of the egg length (EL) in the anteroposterior direction (0% EL = posterior pole). Within this area, the anlagen for the three thoracic and eight abdominal segments are equally spaced, each occupying a transverse stripe of a width of about 3.9 EL, corresponding to three to four cell diameters. The region of the blastoderm from which the epidermis of these segments develops comprises about 2200 cells which is one-third of the cells of the blastoderm. The paper includes a detailed description of the cuticular pattern of aDrosophila melanogaster first-instar larva.
