Printed in Great Britain The relation between larval and

Early embryonic stages of Calliphora erythrocephala were X-irradiated to produce ab-dominal abnormalities of segmental pattern. Abnormal patterns were examined in the puparial stage: 75 (Series AA) larvae with dorsal or lateral abnormality were classified and the larval abnormality compared with the pattern of abdominal segmentation in the emerging adult fly; another 75 (Series aa) larvae were examined in dorsal, lateral and ventral aspect with respect to segmental abnormality and again in relation to abnormality in the adult. It was observed (i) that the pattern of abdominal intersegmental membranes is not necessarily maintained through metamorphosis and may regulate to normal; (ii) that tergal abnormalities in the adult result from a failure of correct bilateral fusion of corresponding contralateral hemitergites; (iii) that reduction or displacement of scleral structures in an adult abdominal segment is correlated with deficiency or displacement of epidermal muscle insertions, and hence presumably with the histoblast anlagen which are normally associated with them. In the case of dorsal abnormalities, hemitergite differentiation is normal. Larval abdominal abnormality patterns point to the mode of bilateral morphogenesis of the germbands in embryogenesis. The relation of adult to larval abnormalities suggests some similar independence of contralateral hemisegments at metamorphosis. The possible developmental origin of abdominal abnormalities produced by X-irradiation of embryos is discussed, and the conclusions of the analysis of the relation between larval and adult abnormalities in Calliphora are set against the propositions of previous students of such abnormalities in Drosophila