STAGE 15. Age 17 ½ h.; length 1.5 -1.6 mm.

Ext. Crit.: *Early neural fold stage*. *Presumptive cement gland faintly circumscribed*. *Anterior part of neural plate roundish*. *Neural folds distinct*, except medio-rostrally; *initial formation of sharp inner ridges on neural folds* in rhombencephalic region.

Int. Crit.: *Cement gland anlage delimited*. First symptoms of segregation of neural crest from thickening and narrow neural plate (s.s.). *Presumptive eye anlagen begining to sink in*.

Beginning of dorsal convergence and stretching movements. Clearly discernable myocoel.

Blastocoel disappeared or greatly reduced.