Windowing chicken eggs allows you to observe and manipulate the living embryo.
Watch this five minutes video explaining the windowing process:
Lay the eggs sideways in the incubator and mark the uppermost surface of the egg with an X. The yolk will pivot so that its lightest point, the embryonic blastoderm, will rotate from beneath the airspace to the highest point. The X will, therefore, indicate the location of the embryo.
Incubate the eggs at high relative humidity (>50 %) and in the range of 37.5 to 39oC.
Follow these steps for the windowing:
Wipe the egg with 70% ethanol to avoid contaminations.
Pierce the blunt end of the egg with the point of a scalpel, thereby opening an air space.
Insert a 19 g needle on a 5 mL syringe through the hole, direct the tip of the needle towards the bottom and withdraw 2-4 mL of thin albumen.
Cover the top side of the egg with clear sticky tape.
With the point of your scissors drill a hole in the middle of the X to admit air.
Leave the egg aside for a few moments while the embryo which is immediately beneath the shell subsides into the space created by the withdrawal of albumen.
Use the scissors to make a circular cut in the shell about 15 mm in diameter directly over the blastoderm. Do not make a complete cut but leave a strip of the shell and sticky tape so that you can flip back the cut shell.
Now you are ready to observe the embryo under the stereo microscope. Make sure you tape the window before incubation otherwise the egg will dry out.