NF stage 20

^ http://purl.obolibrary.org/obo/XAO_1000036

Nieuwkoop and Faber stage 20, corresponding to an embryo of age 21 hr 45 min at 22-24 Celsius and having the following external morphological criteria: Neural folds fused, suture still present. The two eye anlagen showing through dumb-bell-shaped, eyes hardly protruding. Beginning of stretching of embryos. Lateral outline flat. Length: 1.7 - 1.8 mm. [ https://www.worldcat.org/search?q=bn%3A0815318960 ]