Key events: germ band elongates to 75% egg length, stomodeum invaginates

Stage 10 lasts for about 1 h (4:20-5:20 h). The onset of this stage is characterized by the appearance of the stomodeum, which eventually gives rise to the foregut and its annexes.


The stomodeum develops from the stomodeal cell plate located on the ventral side near to the anterior pole of the embryo. All cells of the stomodeal plate start to divide at approximately the same time and the plate sinks inward. After only one round of mitoses, cell division is transienly interrupted. The stomodeal cells are arranged as a regular monolayered epithelium. This epithelium tilts posteriorly and establishes contact with the cell mass of the anterior midgut primordium.

The germ band continues to stretch, reaching its maximum extent towards the end of stage 10 at about 75% egg length (0% egg length = posterior pole). The interior of the egg is occupied by the yolk sac, which extends into the procephalic region. During late stage 10, all pole cells leave the cavity of the posterior midgut, and come to lie dorsally on both sides of the posterior midgut primordium, outside the yolk sac.

In stage 10 parasegmental grooves also appear in the trunk region of the epidermis. Within the territory of the germ band, segregated neuroblasts have started dividing according to a characteristic asymmetrical pattern. Neuroblasts divide to produce smaller daughter cells, so-called ganglion mother cells, which remain distal to the dividing neuroblasts. This arrangement is due to the polarity of divisions, with the mitotic spindle oriented perpendicular to the embryonic surface.

Ten tracheal placodes appear, which are recognizable as slight pits in the laterodorsal region of the prospective dorsal epidermis.