day 6
implantation
day 16
gastrulation
day 18
neural plate forms
day 20
first somite forms
day 22
neural tube begins to close and heart begins to beat
day 24
cranial neuropore closes
day 26
caudal neuropore closes
week 2
primordial germ cells arise from the epiblast
week 3
primordial germ gells in the yolk sac
week 12
blood formation involves the spleen
week 30
blood formation shifts to marrow
week 9
blood formation begins in liver