EGGS AND INCUBATION 351 



on the twelfth. The entire shell except the air cell is occu- 

 pied by the chick by the twelfth day. The feathers appeal- 

 first on the eighth day, and by the thirteenth cover the body 

 to the length of one-fourth inch. At this time the nails of 

 the feet appear. On the fourteenth day the chick changes 

 its position and extends lengthwise, the beak reaching the 

 inner shell membrane. The air cell has been gradually 

 increasing in size, and by this time is much larger. From now 

 on, the chick increases in development to the twenty-first 

 day. The" following interesting description of the hatching 

 process is given by Professor Lewis:* 



"When ready to come out, the chick raises its head and 

 pierces the inner shell membrane, and immediately starts 

 breathing the air in the chamber, which causes the pulmonary 

 circulation to become active and the embryonic circulation 

 to cease. The head is next raised into the air chamber, and 

 the chick deals blows upon the shell, which when often 

 repeated in the same place result in fracturing it. This 

 process is repeated until the shell is broken around about 

 one-third of the way from the large end. The chick then 

 presses its head against the large end and its feet against the 

 small end, and then by pushing is able to throw off the shell 

 lid and make its exit." 



The temperature of the egg during incubation should be 

 about 103 degrees. The usual temperature of the body of 

 the hen is 106 degrees, and her eggs from 102 to 104 degrees. 

 The egg must be kept close to this temperature, and serious 

 variation from this will kill the chick in the egg. During 

 the first week a temperature of 102 is best, but this may 

 increase to 103 degrees the last part of incubation. After 

 the third or fourth day the eggs being incubated should be 

 turned once or twice daily. 



Poultry Laboratory Guide, 1910, p. 47. 



