STAGE 24. Age 1 d., 2 ¼ h.; length 2.5-2.7 mm.

Ext. Crit.: *Eyes protruding less far lateral than gill-area*. *Gill-area more prominent than jaw-area*, gill-area not yet grooved. Ventral outline of embryo nicked. Tail bud discernible. Initial motor reactions to external stimulation.

Int. Crit.: Distinct nerve fibers in root of trigeminus nerve, and some fibers emerging from gangl. profundus and Gasseri. Medio-lateral contriction of central canal extended over 2/3 of spinal cord, and *anterior half of spinal cord completed*.
*15 somites segregated*; axial mesenchyme becoming liberated from somites. Tail bud for the first time distinct. Segregation of collecting tube anlage in anterior portion of pronephros.
Segregation of hypochorda starting anteriorly.