STAGE 18. Age 19 ¾ h.; length 1.5 -1.6 mm.

Ext. Crit.:*Neural groove stage*. *Anterior part of neural plate narrow, more or less club-shaped*, ofter narrower towards rostral end. *Parallel neural folds in trunk region very close to each other*, not yet touching.

Int. Crit.:*First segregation of mes- and rhombencephalic neural crest*. Eye evaginations with slit-shaped cavities.
*Anterior 3-4 somites in process of segregation*.