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| Chick embryo at stage 11 (approx. 2 days old), somites and optic lobes are visible. | Chick embryo at stage 16 (approx. 3 days old), somites, brain, eye, and heart are visible. | Chick embryo at stage 21+ (approx. 4 days old), brain, eye, heart, limb bud, and allantois are visible. |