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glandular wall of the oviduct secretes much of the albumen or 

 ''white" around the egg. In the lower part of the oviduct, the 

 shell membranes are added, and the calcareous shell is deposited in 

 part here and completed in the uterus and vagina. The time re- 

 quired for the egg to pass from the ovary to the exterior at laying 

 averages about twenty-two hours. The average-sized hen's egg 

 weighs about two ounces of which 11 per cent is shell, 32 per cent 

 yolk, and 57 per cent albumen. A dozen or fifteen eggs are usually 

 laid in the same nest by the hen and then incubated with her body 

 temperature by sitting on them almost constantly for twenty-one 

 days. They are kept at a temperature between 98° F. and 100° F., 

 and are turned over each day to avoid internal adhesion of the 

 embryo to shell membranes. At the end of this period they hatch 

 by breaking through the shell with the temporary "egg tooth" on 

 the beak. The chicks are covered with down, have their eyes open, 

 and can run as soon as they are dry. For this reason they are said 

 to be precocial, and since they leave the nest immediately, they belong 

 to a general group called the nidifugae. Another type of bird which 

 requires parental care, such as feeding, is said to be altricial, and 

 since it remains in the nest, it belongs to the group nidicolae. The 

 individual reaches maturity in from six to ten months, depending 

 on the breed. 



