ABSTRACT
A developmental abnormality characterized most obviously by longitudinal contraction of the embryo occurred in high frequency (up to 70 per cent.) among eggs from females of a selected line of the beetle Dermestes maculatus.
In the majority of the abnormal embryos dorsal closure does not occur and the embryonic material forms a boat-shaped structure beneath the yolk. Stomo-daeal and proctodaeal invaginations are formed, but the endodermal wall of the mid-gut is absent.
Development is abnormal from the time of blastoderm formation. The blastoderm is not completely cut off from the underlying yolk plasmodium, to which it remains connected by strands of cytoplasm.
It is suggested that the failure of the yolk plasmodium to become clearly separated from the blastoderm accounts for the contraction of the embryo and also for the absence of the endodermal layer.
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