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
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.
Time table of embryogenesis..........additional information
Embryogenesis, in vivo (6.6 MB)
Chorion (0.2 MB)
Chorion, interactive (3.2 MB)
Eggshell (0.7 MB)