206 THE LIFE OF A BIRD. 



the broad half of an egg-shell which has been 

 broken open for domestic use, and then, in looking 

 at the inside, the partition membrane will be seen, 

 and may be lifted on the point of a pen-knife; the 

 little cavity beneath is then rendered distinct. 



It is difficult to state what is the precise use of 

 this air-chamber. It was formerly, and may be 

 still by some, regarded as essentially necessary for 

 the respiration, so to speak, of the developing 

 bird. But some experiments, to which allusion 

 will again be made, appear to show that such can- 

 not be its real office. As the bird in the shell 

 undergoes its early developments, this air-chamber 

 increases in size ; it increases also if the egg is 

 not in progress of hatching, and from a cause to 

 which we have before alluded. 



The lining membrane of the shell has been de- 

 scribed to consist of two layers. In order to 

 ascertain this, more skill in anatomical investiga- 

 tion is requisite than most persons possess, and 

 under those circumstances they must be content 

 to take the statement on the good authority with 

 which it can be offered for acceptance. In the 

 fresh egg this membrane is thin, semi-transparent, 

 and very easily torn ; but during hatching it be- 



