Day One (after fertilization):

• Initial nuclear and cytoplasmic divisions.
• meroblastic cleavage patterns
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Day Two:

• heart, forbrain, and eye structures begin to develop
• somites visible
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Day Three:

• embryo turns to its side, exposing its heart tube
• limb bud formation begins
• begins to curve its back
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Day Three and a Half:

• further development of the eye, brain, and heart are visible
• limb buds enlarged
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Day Four:

• limb buds elongate
• red coloring is blood
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Sources:

Gilbert, SF. Developmental Biology 6th ed., 2000. Sinauer Associates Inc., Sunderland, MA.

Hamburger, V and Hamilton, H. 1951. A series of normal stages in the development of the chick embryo. J Morphol. 88:49-92.