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Aust. J. Zool.



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Development of the egg of D. violescens commences as nuciei multiply and congregate at the posterior pole (stage I A). A germ disk then forms which elongates and becomes segmented as it turns anticlockwise on the surface of the yolk. Anatrepsis is completed when the tail end of the embryo reaches almost halfway to the anterior pole on the micropylar side of the egg. Katatrepsis commences as the embryo moves head-first around the posterior pole and continues to differentiate. The process is completed when the head of the pharate first-instar nymph comes to rest beneath the operculum al the anterior pole of the egg. Eggs kept at a constant warm-temperature enter first diapause when there are numerous nuclei at the posterior pole (stage 1 A of embryology), and if held under these conditions for a prolonged period they may emerge from diapause irregularly and continue development. In the field eggs develop continuously but slowly, suggesting that diapause and embryogenesis may proceed together at temperatures favourable to both.

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