  We propose a 2D mechanical model of the ventral furrow formation in
Drosophila that is based on undifferentiated epithelial cells of identical
properties whose energy resides in their membrane. Depending on the relative
tensions of the apical, basal, and lateral sides, the minimal-energy states of
the embryo cross-section includes circular, elliptical, biconcave, and buckled
furrow shapes. We discuss the possible shape transformation consistent with
reported experimental observations, arguing that generic collective mechanics
may play an important role in the embryonic development in Drosophila.
