HOW THE SHAPE OF AN EGG IS DETERMINED 395 



treme cases a fowl so afflicted will crawl with her body upright 

 and her tail dragging on the ground. 



The shape of an egg is largely determined by the contours in 

 the oviduct in which it is cast. During the passage of the yolk 

 in the oviduct it is pushed forward by the muscles of this 

 tissue, at the same time receiving a deposit of albumen. The 

 oviduct being twisted and contracted, imparts a turning motion 

 to the yolk as it advances, which causes the albumen to be formed 

 in layers. These layers are sometimes visible in a raw egg, but 

 are better seen in a hard-boiled egg. 



Chalaza. — Two principal cords or fibers, technically known as 

 the chalaza, support the yolk in about the center of the al- 

 buminous mass, and serve to protect the yolk from injury by 

 undue jarring or rough handling. See Fig. 258. We have all 

 noticed, perhaps, that whatever way an egg is turned the yolk 

 quickly assumes its original position ; this is due to the influence 

 of the chalaza, and to the fact that the yolk, containing a large 

 amount of fat, which is lighter than the albumen, has a tendency 

 to float upward. 



Shell Membrane. — When sufficient albumen has been se- 

 creted, at which time the entire mass has reached the lower part 

 of the oviduct, the shell membrane is formed, after which it 

 passes still further and the outer membrane is added. Here, 

 glands which contain a secretion of carbonate of lime and other 

 mineral substances, also the color pigment, deposit their liquid, 

 which quickly hardens the outer membrane. This hardening 

 process is very rapid, and frequently takes place while the hen is 

 on the nest. 



Bloom of the Egg. — ^The egg has now reached the lowest part 

 of the oviduct, known as the cloaca, whence it is ready to be laid. 

 While in this section it is covered with an oily secretion which, 

 as previously mentioned, aids in the delivery of the egg. This 

 secretion dries almost immediately the egg is laid, and gives it 

 the bloom or fresh appearance found in a newly laid egg. When 

 eggs are washed this bloom is destroyed, or partly so, which 

 makes washed eggs rather easily detected by experienced handlers. 



