146 THE STRUCTURE OF THE FOWL 



Baer. Some time about the fourteenth day 

 the chick arranges itself lengthwise within 

 the egg so that the head is towards the broad 

 end and near the air-chamber. The head is 

 bent upon the chest and usually tucked under 

 the right wing. A few days later the neck 

 assumes a double curve which brings the head 

 forwards and the beak close to the inner shell- 

 membrane enclosing the air-chamber. During 

 this change the amniotic fluid diminishes in 

 quantity. About the fifteenth day the coils 

 of intestine, previously protruding through 

 the umbilicus, are withdrawn into the abdomen. 

 On the nineteenth day the yolk-sac also begins 

 to retract, and by the twentieth day has 

 entirely entered the abdomen. Thereupon the 

 umbilicus becomes occluded. 



On the twentieth day also the chick thrusts 

 its beak- — armed with a horny excrescence 

 known as the " egg-tooth "^ — through the inner 

 shell - membrane into the air-chamber, and 

 begins to breathe by the lungs. The function 

 of the allantois now being superseded, the 

 umbilical vessels become occluded, and the 

 membrane shrivels up and becomes detached 

 at the umbilicus. That breathing by the lungs 

 is initiated some time (possibly two days) 



