STRUCTURE OF THE SHELL. 195 



we're connected together by mucus. But the in- 

 quiries of Dr. Dickie* appear to show that the 

 egg-shell is much more highly organized than had 

 been supposed that it is really a very beautifully 

 formed and even complicated structure. From 

 his inquiries it appears that the shell has the same 

 general arrangement of parts as the skin, or the 

 mucous membrane lining the internal surface of 

 the body. To most persons it is a familiar fact 

 that, overlaying the true skin, is what is called the 

 scarf-skin, a thin scaly covering which protects 

 the exquisitely tender and delicate surface of the 

 true skin beneath, and without which the sensation 

 of touch would be agony too great for endurance. 

 Now the egg-shell has a somewhat similar arrange- 

 ment of its parts ; outwardly there is a layer or a 

 series of layers, which corresponds to the scarf- 

 skin of our own bodies, and underneath this layer 

 or layers is another very fine and delicate mem- 

 brane, which corresponds to a similar membrane 

 just above the true skin in the body, and is called 

 the basement membrane. By macerating eggs in 

 a dilute acid, shreds of a fine membrane can often 

 be detached, which, when examined under the 

 * Annals of Natural History, 



