196 THE LIFE OF A BIRD. 



microscope, are seen to be full of small cells ; this 

 is the surface membrane, and underneath it, were 

 we sufficiently expert in microscopic manipulation, 

 we might detect the finer membranous structure, 

 called, in the language of physiology, by the name 

 of the basement membrane. 



The superficial membrane varies very much in 

 different eggs, and its variation is the cause, in 



many cases, of the difference in the appearance 

 of the eggs. Its appearance in the shells of the 



