The embryonic development of Drosophila melanogaster has been subdivided into 17 stages by Volker Hartenstein and José Campos-Ortega. Staging according to these authors has become a general reference in Drosophila research.



Embryonic stages are defined by prominent features that are easily distinguishable in the living Drosophila embryo. The duration of the various stages indicated in the text refers to embryos developing at 25°C. We wish to emphasize that most of the data described here are average values obtained from observations on several different embryos. Due to difficulties in precisely defining the beginning and end of most of the relevant stages, there is some variability in the timing of stages, so that the times given in the following documents should be understood as approximations.

The egg is bilaterally symmetrical, and distinction between the dorsal and ventral surfaces is indicated by differences in curvature, for the dorsal side is flattened while the ventral side is somewhat convex. The dimensions of the egg are variable; an average length is 500 µm, the diameter is about 180 µm.

The mature egg is enclosed by two envelopes, an inner homogeneous vitelline membrane and an outer tough, opaque chorion. The chorion is not structureless but rather ornamented with hexagonal and pentagonal figures. These ornamental markings represent the impressions of the ovarian follicle cells on the originally soft, plastic membrane secreted by the follicular epithelium. Paired delicate filaments – extensions of the chorion – are situated on the dorsal surface not far from the anterior end of the egg. The micropylar opening for the passage of sperm is generated by the vitelline membrane. It indicates the anterior pole of the embryo.

When the chorion is removed one may directly observe certain aspects of the developmental processes through the transparent, structureless vitelline membrane, which is closely apposed to the protoplasmic contents (see also the time lapse movie "Embryogenesis, in vivo").

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