NESTS. 



147 



the bottom of the same canal. The eggs are hatched by 

 being kept at a temperature of 10i Fahr. By a beautiful 



FIG. 165. 



Fibrous membrane from au Egg-shell, Magnified. 



arrangement the yolk and its germ are always kept in the 

 right position, no matter which side up the egg may be. 



The young bird has a horny point at the extremity of 

 the bill, with which it breaks the shell ; this falls off a few 

 days after the bird is hatched. 



Professor J. W. P. Jenks has recently discovered that the shell is 

 first pierced by the forward and backward motion of the under man- 

 dible, and the aperture thus made is then enlarged and the shell 

 broken by the upper mandible and its horny point. 



Most birds build nests in which to lay their eggs ; and it 

 is an interesting fact that all individuals of a species build 

 essentially alike, and, in a given locality, of the same 

 kinds of materials. Their skill and industry in nest-build- 

 ing are truly wonderful. Some kinds build with sticks; 

 others with dried grasses and hair ; others with mud and 

 dried grasses; others mainly with the woolly covering of 

 the stalks of ferns ; others, as some kinds of Humming- 

 birds, largely with lichens; and so on, through a long list 

 of materials that might be enumerated, but which it is not 

 necessary to enumerate here. Some kinds, like the Oriole, 



