PROGRESSIVE POULTRY CULTURE 53 



inch from its lower edge and on the side opposite the 

 branch tube, to supply air from below. 



In ordinary testing, which is done in a dark room 

 during incubation, each egg is held successively against 

 the hole in the cloth, at the end of the branch tube, the 

 strong light of the tester penetrating the egg and making 

 its contents more or less visible to the operator. The 

 latter may observe the egg from one side if he prefers 

 and thus relieve the eyes from looking directly towards 

 the light of the tester. 



In studying the development of the embryo and the 

 appearance of the various parts of the egg, the latter 

 may be held against the egg-hole of the tester in dif- 

 ferent positions to facilitate observation. 



THE SUCCESSIVE STAGES OF INCUBATION. 



Selected white-shelled eggs are placed, some under 

 broody hens and some in an incubator if one is avail- 

 able, so as to compare eggs naturally and artificially in- 

 cubated, while studying the successive stages of the de- 

 velopment of the embryo chicks in the egg. 



At the end of twenty-four hours of incubation a 

 change can be detected in the fertile egg held before the 

 egg-tester, if its search-light is very strong and the shell 

 of the egg thin and white or nearly transparent. By cell 

 division and multiplication the germ's surface or skin 

 (blastoderm) has increased in size and shows against 

 the faint yolk-shadow as a small shadow-circle (about 

 one-half inch in diameter), having a slightly reddish or 

 rosy tint. 



At the end of another day the circle has increased 

 in size to three-fourths of an inch or perhaps an inch 

 in diameter and the tint is of slightly deeper tinge. 



After seventy-two hours of incubating the blastoderm 

 shows a decidedly bright reddish color especially if the 

 shell of the egg is nearly transparent. Its size has in- 

 creased to about one and one-quarter inches. The cen- 

 tral portion appears slightly lighter than the parts at 

 and near the circumference. 



By holding an egg, during the early stages of in- 



