The origin and structure of the secondary coat of the egg of Drosophila melanogaster

Summary The techniques of light and electron microscopy have been employed in a study of the protective coverings of the egg of Drosophila melanogaster. Data obtained during this investigation suggest the involvement of the follicle cells, in the production of one of these coverings and justify its classification as a secondary coat. The secondary coat of D. melanogaster is highly organized and has been divided into three Zones (I, II, IIII). The follicle cells enveloping the oocyte exhibit two phases of secretory activity each involving hypertrophy of the Golgi complex and rough endoplasmic reticulum, and the production of protein and polysaccharide components. The first phase concerns the elaboration of the material which gives rise to the homogeneous lamina referred to as Zone I. The second results in the release of an electron dense component which becomes organized into two laminae separated by struts or pillars; this construction is referred to as Zone II. At the completion of this secretory phase, the follicle cells assume a squamous morphology and a third Zone, composed of a homogeneous substance, appears between the follicle cells and Zone II.This investigation was supported by grant GM-08776 to one of us (EA) from the National Institutes of Health, United States Public Health Service.