An Inherited Abnormality Affecting the Development of the Yolk Plasmodium and Endoderm in Dermestes Maculatus (coleoptera).

IN a previous paper (Ede & Rogers, 1964) a method was described for obtaining lines of the beetle Dermestes maculatus in which a large proportion of eggs produced specific abnormalities which could be used in investigations into its embryology. One of these abnormalities, type G, occurred in high frequency (up to 70 per cent) in a selected line, and was therefore particularly suitable for further study. Not enough genetic information was obtained to show how it was inherited, but it was sufficient for the purpose of an embryological investigation that it should persist through the three generations over which the stock was maintained. Though developing so abnormally that they never emerge from the egg, these embryos live up to and slightly beyond the time at which normals hatch. At this time they are generally extremely contracted, and the endoderm, which forms the wall of the midgut in normals, is completely absent. The origin of the abnormality can be traced back to an early stage of embryogenesis when the superficial cellular blastoderm is becoming separated from the' yolk plasmodium' beneath it. These features give it a particular interest, for the origin of the midgut has always presented problems for insect embryologists (Henson, 1946), and the yolk plasmodium plays an active and important part in a number of developmental processes (Counce, 1961; Krause & Sander, 1962). The present study throws light on both these topics.