134 POULTRY BREEDING 
of the nest with the larger end highest, which is the most 
favorable position for hatching. The shell is composed 
of calcareous material arranged in minute crystals be- 
tween which there are openings through which the air 
can pass from the outside, and the carbon dioxide, elim- 
inated in the process of incubation, can pass outside. 
SECTION OF AN EGG, 
A, Shell; B, Airspace; C, Shell Membrane; D, White; E, Vitelline Membrane; 
F, Yolk; G, Germinal Vesicle; H, Chalaza. 
Next the shell is an exceedingly tough fibrous lining, 
made up of thread-like fibers, crossing each other in every 
conceivable direction. At the larger end of the eggs this 
fibrous lining separates into two parts, one of which fol- 
lows the shape of the shell and the other is depressed so 
as to form a sack or empty space, called the air-bubble 
or air-space. Immediately inside the shell membrane, is 
the white, mostly albumen and water, and suspended in 
the white is the yolk, which is more than one-third fat 
