Table 1. Stages of early embryogenesis

Stage	Embryonic state	Timing (hpf^a)	Notes
1	Egg
2	Two-cell	1.5
3	Four-cell	2
4	Eight-cell	2.5
5	16-32 cell	3
6	Morula	3.5
7	Early blastula	4
8	Midblastula	5-6
9	Late blastula	6-7
10	Early gastrula	8-9
11	Midgastrula	13-15
12	Late gastrula	15-20
13	Early neurula	20-22	Yolk plug is completely internalized; neural plate becomes apparent.
14	Midneurula	23-25	Neural fold forms.
15	Late neurula	24-26	Neural plate starts to close at the posterior part.
16	Late neurula	27-28	Neural tube is closed in the posterior half.
17	Late neurula	27-29	Neural tube is closed, except for wide-shaped brain region.
18	Late neurula	28-30	Neural tube is closed, except for narrow-shaped brain region.
19	Late neurula	29-31	Entire neural tube is closed, but the midline where left and right neural folds meet is evident.
20	Tailbud	30-32	Neural folds are completely fused, losing the midline; tailbud forms.

^ahpf: Hours post-fertilization.