STAGE 22. Age 24 h. (= 1 day); length 2.0-2.2 mm.

Ext. Crit.: *Distinct protrusion of eyes*. *Initial groove between jaw- and gill-areas* only at latero-dorsal side. Lateral and ventral outlines of embryo slightly concave. Anal opening displaced to ventral side. Vitelline membrane becoming wider.

Int. Crit.: First indication of formation of doso-lateral placodes in sensorial layer of ectoderm. *Segregation of brain in pros-, mes- and rhombencephalon*; cephalic flexure approximately 135°. In anterior spinal cord beginning of medio-lateral constriction of central canal and withdrawal of anterior trunk neural crest. Primary eye vesicles in broad contact with epidermis. *Segregation of hyal portion of mesectoderm*. *Anterior 9-10 somites distinct*. Formation of blood islands indicated.