part of preceded by neurula stage NF stage 18 NF stage 19 XAO:1000035 xenopus_developmental_stage Nieuwkoop and Faber stage 19, corresponding to an embryo of age 20 hr 45 min at 22-24 Celsius and having 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. NF stage