Definition: Nieuwkoop and Faber stage 19; age 20 hr 45 min at 22-24 Celsius; corresponding to the following external morphological criteria: Initial neural tube stage. Neural folds touching each other, except for inconstant openings at anterior and posterior end and behind nucal region. Considerable lateral extension of brain. Lateral outline of embryo still convex. Length: 1.5 - 1.6 mm.