[Development of the malformation "double abdomen" in eggs of smittia parthenogenetica (dipt., chironomidae) partially irradiated by UV].

UV-irradiation (maximum intensity at 253,7 nm) of the anterior 1/3 of the egg during nuclear migration stage frequently is followed by the formation of "double abdomens". The type of malformation shows a germ band in which head, thorax and anterior abdominal segments are replaced by a set of 6-8 posterior abdominal segments joined in mirror-image symmetry to the corresponding parts of the original abdomen. The course of development leading to this malformation is visibly aberrant from the blastoderm stage to germ band segmentation only. The two abdomens develop in strict synchrony provided their positions are symmetrical to the equatorial plane of the egg. Asymmetric positions are less frequent and delay temporarily the development of one or the other of the abdomens due to the lack of space. The results are compared to similar malformations in other insect eggs and possible interpretations are reviewed.