10 days: Two fluid cavities, yolk sac and amnion sac, develop inside cell sphere {chorion} {gastrula}.
10 days: Two fluid cavities develop inside gastrula. Fluid cavities {amnion sac}| can have ectoderm inside.
10 days: Two fluid cavities develop inside gastrula. Fluid cavities {yolk sac}| can have endoderm inside, to later make primitive gut.
10 days: Yolk sac has endoderm {primitive gut} inside.
10 days: In hard-shell eggs, one cavity {subgerminal space} is away from yolk, under dividing cells.
4-Zoology-Development-Stages-Gestation
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Date Modified: 2022.0225