302 GENERAL SCIENCE 



this case as in cold storage the eggs should be turned from 

 time to time that the yolk may not settle to one side and 

 become attached to the shell. Brooding hens turn the eggs 

 upon which they are sitting, and when eggs are hatched in 

 an incubator they must be turned one or more times. 



SUMMARY 



The hen as type of all domestic fowls illustrates the modifications 

 accomplished in animal structures by long-continued selective breeding. 

 Certain characteristics in build, coloring, and egg production have been 

 intensified by retaining in the flocks year after year only those fowls 

 which exhibit the desired characteristics in most marked degree. 



If domesticated fowls were turned loose and allowed to run wild in an 

 uninhabited region, few if any of them would be likely to survive the 

 conditions for which they long before had become unfitted. It is 

 likely, however, that if any should survive their successive generations 

 would rapidly revert to the smaller more active forms seen in the differ- 

 ent kinds of game birds. 



A study of the skeleton of a hen in comparison with the skeleton of 

 a human being shows that the hen walks on her toes. The lower, scaly, 

 and often featherless part of the leg corresponds to the human foot. 



Where fowls are kept too closely penned up, and without sufficient 

 freedom of range, they are less hardy, more likely to sicken and die, and 

 are often infested with vermin. Shelter from cold and wet is essential 

 to their healthy state. 



Most of the contents within an egg is material for the nourishment 

 and growth of the embryo. The chick in due time, when the necessary 

 conditions for hatching have been favorable, acquires the strength to 

 break the shell enclosing it and to make its way out. 



The growth of the young chick from the embryo stage is by cell 

 division just as growth occurs in the human body and in plants. A 

 wonderful thing about it, however, is the variety of the organs (masses 

 of cells doing the same kind of work in the body) that are made out of 

 the material stored in an egg. 



Eggs may have in them all this stored material and yet be worthless 

 for the hatching of chickens because destitute of the embryo. Its 

 development when the egg is forming involves fertilization, which cor- 

 responds to the fertilization of the ovules of flowers (page 265). Seeds 



