STAGE 20. Age 21 ¾ h.; length 1.7-1.8 mm.

Ext. Crit.: *Neural folds fused, suture still present*. The two eye anlagen showing through dumb-bell-shaped; eyes hardly protruding. Beginning of stretching of embryo. Lateral outline flat.

Int. Crit.: Embryonic pigment of epithelial layer of ectoderm concentrated at apical side of cells. Stomodeal-hypophyseal anlage indicated by median thickening of sensorial layer of ectoderm just in front of brain. *Brain subdivided into arch- and deuterencephalon*. Massive neural crest extending anteriroly approximatedly to anterior border of eye anlagen. In trunk region neural crest still in contact with suture of closing neural tube.
*Anterior 6-7 somites segregated*. Coelomic cavity indicated in most dorsal portion of lateral plate.
Anlage of hypochorda indicated. *First indications of 1^st and 2^nd visceral pouches in pharyngeal wall*; oral evagination visible.