Sequence of light micrographs of an inverting V. globator embryo in situ and in vivo. Time-lapse sequence of a single living embryo inside its parental spheroid. The embryo was captured in side view at 3.5-min intervals throughout inversion. (A) The embryo 3.5 min before the initiation of inversion. (B) Inversion begins with the contraction of the posterior hemisphere. (C to F) 3.5 min, 7 min, 10.5 min and 14 min after the initiation of inversion; contraction proceeds and accompanies movement of the posterior hemisphere into the anterior hemisphere; invagination of the cell sheet generates a ring of maximum curvature between the two hemispheres. (G to K) 17.5 min, 21 min, 24.5 min, 28 min and 31.5 min after initiation of inversion; the posterior hemisphere lies completely within the anterior hemisphere but moves further still toward the anterior pole; the phialopore appears at the anterior pole and widens continuously. (H to L) 21 min, 24.5 min, 28 min, 31.5 min and 35 min after the initiation of inversion; the widening of the phialopore proceeds and the anterior hemisphere moves over the already inverted posterior hemisphere. (L to O) 35 min, 38.5 min, 42 min and 45.5 min after the initiation of inversion; the last third of the anterior hemisphere moves over the already inverted cell monolayer. (O,P) 45.5 min and 49 min after the initiation of inversion; inversion ends with the closure of the phialopore. Directions of cell layer movements are indicated by black arrows. Scale bars: 20 μm.