320 



Nature-Study Agriculture 



Develop- 

 ment of 

 the embryo 

 chick 



u. s. D. A. 



FIGS. 262 and 263. Figure 262 (above) shows a fertile and an infertile egg after 

 both had been kept for 24 hours at the temperature required for incubation 

 (about 103 F.). Figure 263 (below) shows a fertile and an infertile egg 

 after both had been kept at this temperature for seven days. 



from entering. A supply of air for the chick is stored 

 at the large end of the egg. 



Within less than a day after an egg has been set, the 

 tiny germ has begun to grow (Figs. 262 and 263), 

 and it is quite noticeable if the egg is broken and ex- 

 amined. In two days the heart, which has now 

 begun to beat, is sending blood through a network 

 of fine arteries and veins. In four days wings and 

 legs begin to develop. The feathers begin to appear on 



