At stage 11, the parts of the foregut primordium giving rise to the proventriculus (pv) and the adjacent esophagus (es) have invaginated. They form the stomodeum. The primordia of the salivary glands (sg) invaginate from the ventral labial segment. The posterior midgut rudiment (pmg), after its cells performed the third postblastoderm division, has lost its epithelial characteristics and now forms a solid cluster of rounded cells equal to those of the anterior midgut rudiment (amg), Four spherical evaginations, which will form the Malpighian tubules (mp), appear in the hindgut primordium close to its boundary to the posterior midgut rudiment (see Skaer, this volume).

During stage 12, a significant reorganization of the midgut rudiments takes place. First, both anterior and posterior midgut rudiments stretch in the longitudinal axis and become bilobate. Then, during germ-band retraction, the midgut rudiments approach each other and finally fuse at about 50% egg length.

The midgut primordium of a stage 13 embryo (mg) forms two longitudinal plates of epithelial cells flanking the central yolk. These plates will spread in the transversal axis and eventually
[stage 15] fuse in the ventral and dorsal midline, thereby forming a closed chamber that encloses the yolk. Anteriorly and posteriorly, the plates abut the presumptive proventriculus (pv) and hindgut (hg), respectively. The hindgut has adopted its characteristic sigmoid shape; the Malpighian tubules (mp) have elongated considerably. Anteriorly, the pharynx (ph) starts to invaginate. The gnathal segments, part of which will later form the atrium, have moved anteriorly. (ap) Anal pads; (ms) mesoderm; (sm) somatic mesoderm; (vm) visceral mesoderm.