STAGE 25. Age 1 d., 3 ½ h.; length 2.8-3.0 mm.

Ext. Crit.: *Eyes protruding eually far or further laterally than gill-area*. *Gill-area grooved*. *Invagination of ear vesicle indicated by pigment spot*. *Beginning of fin formation*.

Int. Crit.: Frontal glands indicated in epithelial later of ectoderm of diencephalic region. Cephalic flexure of brain about 90°. First part of n. maxillomandibularis distinct. Most anterior neural crest of spinal cord has begun lateral migration; *only posterior ¼ of spinal cord not yet completed*. Primary eye vesicles fully developed; medial wall decreasing, lateral wall increasing in thickness.
Head somite 1 diminishing; *16 somites segregated*.
*4^th visceral pouch indicated*.