Students can observe the early stages of embryonic development of the chick by growing them in vitro. Experiments have shown that fresh fertile eggs removed from the shell and incubated in sterile glass beakers can be grown to the 9th day. The procedure has its limitations, and therefore requires extreme care. Because the embryos are very fragile during the first few days, the incubator must not be moved. In the unnatural environment, extreme care must be taken to prevent the embryos from drying out from too much evaporation.
Materials Needed
Incubator - one that will maintain 100 - 101 degrees F temperature Fresh fertile eggs Sterile, 100-ml beakers or 4" or 6" PVC pipe (cut in 2-1/2" lengths) Plastic (Saran) wrap Rubber bands
Procedure
To sterilize 100-ml beaker containers, place them in a pressure cooker or saucepan with approximately an inch of water in the bottom. Cover the tops of the containers with wrapping paper held in place with rubber bands.
Maintain 15 pounds of pressure for 15 minutes. Cool the pressure cooker slowly. If a pressure cooker is not available, the containers can be sterilized by boiling for 30 minutes.
If you are using a PVC pipe place a layer of plastic wrap over the pipe extending far enough down the sides of the pipe so that you can place a rubber band over the pipe to hold the plastic in place. With clean hands push the plastic wrap down about 1 1/2" creating a bowl area for the egg to be placed.
Break fresh fertile eggs into the PVC pipe holder or sterile glass containers. Be sure that the germinal disk is facing up. If the germinal disk is on the bottom or side, it will not develop beyond 24 hours. Cover the top of the container with plastic wrap extending far enough down the sides of the container so that a rubber band (2nd rubber band if you are using a PVC pipe) will hold the transparent covering tight against the container. Place the containers in an incubator that will maintain a 100 « 101 degrees F temperature and a high humidity. CAUTION: Do not shake or jar after they have been placed in the incubator.
Results
If the eggs are fertile, all embryos should survive through 24 hours, 85% will survive through 48 hours, 45 - 50% through 72 hours, and 25 - 30% through 96 hours. It is possible for a few eggs to survive for up to 15 days. The primitive streak will become evident at about 16 hours. Blood islands start to form at 24 hours and heart starts to beat at 42 hours. Limb buds begin to form at 62 - 64 hours.
