part of preceded by neurula stage NF stage 14 NF stage 15 xenopus_developmental_stage Nieuwkoop and Faber stage 15, corresponding to an embryo of age 17 hr 30 min at 22-24 Celsius and having the following external morphological criteria: Early neural fold stage. Presumptive cement gland faintly circumscribed. Anterior part of neural plate roundish. Neural folds distinct, except medio-rostrally; initial formation of sharp inner ridges on neural folds in rhombencephalic region. Length: 1.5 - 1.6 mm. XAO:1000025 NF stage