STAGE 2. Age 1 ½ hours; length 1.4 - 1.5 mm.

Ext. Crit.: *Advanced two cell stage*. *First cleavage groove has reached vegetative pole*. Ventral side of blastomeres darker than dorsal side.

Int. Crit.: Penetration of cortical and subcortical layers into interior of egg along cleavage furrow; *the later cutting over about half of egg radius into animal half of egg*. *Formation of very thin partition wall between two blastomeres*; blastomeres not equal in size. First plane of cleavage more or less coinciding with plane of bilateral symmetry.