INCUBATION 41 



breaking an egg each day so as to see how things 

 are going. I told you that the germ of the bird is 

 a round spot of dull white, the cicatricle, which by its 

 mobility is always on top at the surface of the yolk, 

 no matter what the 

 position of the egg. 

 After five or six 

 hours of incubation 

 you can already dis- 

 tinguish in the center 

 of the cicatricle a 

 minute glairy swell- 

 ing which will be the 

 head, and a line 

 which will be the backbone. Pretty soon there be- 

 gins to beat, at regular intervals, the organ most 

 necessary to life, the heart, which chases through a 

 network of fine veins the blood formed, little by little, 

 out of the substance of the yolk, and distributes it 

 everywhere to furnish materials to the other organs 

 just coming into being. It is toward the second day 

 that these first heart-beats, destined to continue 

 henceforth until death, become apparent. Thus irri- 

 gated with running flesh for blood is nothing else 

 this organism thenceforward makes rapid prog- 

 ress. The eyes show themselves and form a large 

 black spot on each side of the head ; the quills of the 

 large feathers form in their sheaths; the scales of 

 the feet are outlined in a bluish tint; the bones, at 

 first gelatinous, acquire firmness by becoming in- 

 crusted with a small quantity of stony matter. 



