STAGE 11. Age 11 ¾ h.; length 1.4 -1.5 mm.

Ext. Crit.: *Horse-shoe-shaped blastopore stage*. Blastopore groove surrounding about half of the future yolk and indicated at its ventral side; future yolk plug often rounded rectangular, slightly elongated in dorsal-ventral direction, *diameter more than 2/5 of diameter of egg (+/- 50° of circumference)*.

Int. Crit.: Mesodermal mantle extending to 30-40° above the equator at dorsal side*, to 20-30° about equator at lateral side and approximately at equator at ventral side. *Invagination of archenteron extended to lateral side; archenteron still slit-shaped, extending dorsally over 40-50°*. Blastocoel beginning to be displaced towards ventral side.