ISO 



POULTRY PRODUCTION 



ni)()n tlic yolk. On the nineteeiitli day wliat remains of 

 tlie yolk is drawn into tlie hody ca\ity. Tiiis apjiears to be 

 tlie most critical day of the incubation ]:)crio(i, for as Payne' 

 has shown, 20 per cent of tlie mortalit,\' ncciirring during 

 the twenty-one days of the incubation period occur on the 

 nineteentli day, and 4S ])er cent of the t<ital i)reliatcliing 

 mortality occur on the eighteenth, ninctcentli, twentieth 

 and twenty-first da>-s. The respirator^' system changes 

 completely on the twentieth day. Until that tune the alhui- 

 tois functions as the chief res] )iratory organ, and, in fact, 

 as tlie excretory organ as well. With the pipping of the shell 

 imlmonary breathing begins. 



Fig. 91 



Appearance of a chick ciiiijryo after forty-eight lioiira in an incnbator 

 (Courlesy of Kan.^as Agiirnltnral iOx|jeiniirnt Station,) 



When formed the chick is placed in the egg with its head 

 L)ent forward beneath the right wing and the legs brought up 

 toward the head. The end of the ui)per mandible of the beak 

 is equipped with a horny cap which bears a sharp point, and 

 by means of this, while slowly revolving in the shell, the chick 

 is able to press against the shell, chipping it in a circular 

 l)ath around the large end of the egg, at the same time 



■ Jour. Am. A.san. Inst, and Lue.st. in foul. IIuslj., vol. vi, No. 2. 



