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METHODS FOR OBSERVING THE DEVELOPMENT 



THE SHELL CAP METHOD: 



This is the method of Price and Fowler (1940). It consists of using a shell from the 

 blunt end of one egg to cover the exposed (blunt) end of an egg from which the shell has 

 been removed. This cover may be removed at periodic intervals, and the embryo ob- 

 served through a much larger aperture than in the case of the cover glass window. There 

 is, of course, added danger of infection. Instead of the shell cap, a fitted glass cap, the 

 edges of which are fastened to the shell, can be used and need not be removed to observe 

 the chick development within. This type of shell cap has the one disadvantage of not 

 allowing free transfer of respiratory gases. 



Save the blunt half of egg shells from any unincubated eggs. The shell membrane should 

 be left in position, and the shells may be sterilized in alcohol, to which a little iodine is 

 added. The cut edges of the shell caps may be made smooth and less brittle by dipping 

 them in melted paraffin. 



Candle a fertilized egg to mark the margin of the air space at the blunt end. Place the 

 fertilized egg in a Syracuse dish with Permoplast base so that the blunt end is uppermost. 

 Clean off the entire blunt end with iodized 95% alcohol, and wipe it dry with sterile cotton. 

 With needle, lancet, or forceps make a small hole in the center of the blunt end and then 

 gradually pick away the shell, making an ever-increasingly large circular hole. It will 

 help to limit the shell cracking if a small hack saw is used to cut a shallow ring around 

 the shell, just within the limit of the air space. The shell should be picked away to within 

 about 1/4 inch of the inner shell membrane and embryo. Pick away all of the outer shell 

 membrane, but remember that this membrane extends completely around the embryo. 

 Avoid ripping or tearing this tough membrane. 



Place a sterile shell cap over the exposed embryo, see that the egg is securely held in 

 the Permoplast of the Syracuse dish, and return the egg to the incubator. The humidity 

 of the incubator must be increased to above 60% for these eggs, since there is a much 

 greater exposed surface for evaporation than in the other method. By the 17th day the 

 egg shell may be sprinkled twice daily with a small amount of sterile water at the incuba- 

 tor temperature, but do not immerse the egg in water. The embryo can be drowned 

 within the shell. 



EXTRA SHELL 



SHELL CAP 



AT BLUNT END, 

 EXPOSED 



MBRYO 

 YOLK MASS 



CHALAZA 



ALBUMEN 



