Thank you to "Purdue Research Foundation" for providing us these photographs.

Both energy and structural materials are needed by the embryo for its development, and these are both provided by  the egg.  During embryonic development, yolk and white (albumen) diminish, with the yolk providing the energy (largely from lipids) and the albumen providing structural proteins and water.
The incubation period is 21 days.

Click on the arrows to go on day by day in the sequence.