202 THE LIFE OF A BIRD. 



bony skeleton of the bird, and various alterations 

 take place in the composition of the yolk and white 

 of the egg. But what appears inexplicable is the 

 assertion of Dr. Prout, that the lime which forms 

 the skeleton of the chick, forming in fact the 

 earthy matter which communicates rigidity to the 

 bones, did not exist previously in the egg, and as 

 he believes was not, therefore, derived from the 

 shell. If this assertion were correct, the circum- 

 stance would tend to upset all the ideas of chemists 

 as to the nature of elements. But it appears pro- 

 bable that the statement is based upon inaccurate 

 data. 



The structure of the rest of the egg must now 

 engage our attention. The white of the egg is 

 enveloped, in addition to the double membrane 

 next the shell, in a delicate membrane proper to 

 it ; a layer of this membrane passing across the 

 broad end of the shell, at a little distance from it, 

 forms the air receptacle exhibited in the preceding 

 diagram. This lining membrane can be prettily 

 shown in the following manner. By employing a 

 very sharp three-cornered file, and acting on the 

 shell with it at a distance of about an inch from 

 the smaller end, the egg may be opened without 



