108 HATCHING AND REARING 



placed in the incubator should be clean and perfect, free from 

 thin porous places, and neither rough nor covered with 

 patches of hard substance. It is most important that the 

 eggs placed in the incubator or under the hen should be 

 average eggs, and perfect in all respects. 



Development of the Chick. The fertile eggs contain, 

 when laid, a germ which has undergone some slight develop- 

 ment. This germ is called the embryo. But nature has 

 ordained that this little germ stop growing as soon as the 

 egg is laid. If, however, the egg is subjected to a tempera- 

 ture of 103 degrees Fahrenheit, it again starts to grow. 

 Placed in the incubator and subjected to this degree of tem- 

 perature, the germ must be kept growing continuously, if 

 the egg is to hatch a strong chick. The direct cause of the 

 incubation of the embryo is steady heat, the incubation 

 temperature being 103 degrees Fahrenheit. 



The growth of the chick within the shell comprises two 

 periods: First, the formative period, in which the various 

 organs and parts of the chicks are formed, this period occu- 

 pying the first three or four days. Secondly, the develop- 

 ment period, which lasts until the twenty-first day. During 

 this time the organs previously formed grow and develop. 



The original embryo in the fertile egg consists of but a few 

 cells, and in its early growth these few cells divide into other 

 cells. From these simple cells a very complicated embryo, 

 with many hundreds of cells, develops in a few days. Each 

 cell develops into a different type of structure. During the 

 first, or formation period, all of the organs of the body take 

 shape. First to appear are the spinal cord and brain, or 

 what will later comprise the nervous system. Next comes 

 the back bone and the ribs. The eye and ear are formed 

 early in the second day. The head and blood vessels make 

 rapid early growth, as the latter must nourish the embryo 

 by carrying to it the food material contained in the yolk. 

 The digestive system is well developed on the third day, at 



