EXERCISE 88 A 

 THE DEVELOPMENT OF THE BIRD EMBRYO DURING THE HATCHING OF THE EGG 



Materials. Two dozen hen's eggs ; an. incubator. 



Directions. Place at least two dozen hen's eggs in an incubator which has previously been in 

 operation until it is properly regulated. Open an egg on at least each of the following days of the 

 incubating period : first day ; second ; third ; fifth ; eighth ; twelfth ; sixteenth. On the first day 

 note the germ cell, or fertilized egg, lying close to the yolk, it being recognized by a reddish ring 

 about it. In the other observations determine what changes have taken place in the eggs. 



Additional problems. Why will eggs usually not hatch after they have been subjected to sudden and 

 great changes in temperature ? Why will eggs not hatch after they have been in cold storage ? 



How do you account for the fact that in a nest of young robins the birds hatch on successive days, 

 while in a nest of quail or domestic fowls the young birds usually all hatch on the same day ? 



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