188 



PO VL rii Y PRO I)U CTION 



tlirmiKli a cliaHgc in jx.stiirc nf tlic liriid .-iikI upper cervical 

 vcrtehnc, chiefly (ic])eii(leiit nii llie imiseiihis l>i\eiiter and 

 nuiseulus spinalis. Tlic ivllcx nieeliani-ni wliicli touelies 

 off this muscle system is ]ii-(>l);ilil\' a ropiratory reflex, not 

 dependent on demand lor o\\-,n'en, l>ut dependent on disten- 

 tion of the ahdomcn . . hron-lit ahout tliron.uh 

 injection of tlie yolk sac (into the hody eaxityl." AVlien tlie 

 shell is nearly cut around a, final eomulsion l>y the cliick 

 flnishes the hreak, and the chick <-an cmci'.ne. 



EmVjriO chick, iuu<1\-.-i\ li'ims did, Mm' wihl^ ami Icl; Ihi'U ciw] lli^- rail 

 fold showing plainly. The liruil i^ .si ill loi-aii'd cii[|.,iile the limly. ^C'ol^■tc■sy 

 of Iowa Agricultural l^xpri imrnl ShLtidii.) 



Selecting Eggs for Hatching. — In selecting eggs for hatching 

 purposes, by far the most important consideration is the 

 health and vigor of the parent stock. The reason why this 

 is so vastly important is fully discussed elsewhere. Suffice 



