298 THE LIFE OF A BIRD. 



hension. It is certainly desirable that a larger 

 number of experiments, similar to those of Mr. 

 Towne, should be made. 



The air contained in the air-follicle is appa- 

 rently intended for the use of the chick as soon as 

 its lungs begin to come into action, which is gene- 

 rally about the nineteenth day. At that period 

 the first evidence of the existence of life within 

 the shell is afforded by the utterance of a feeble 

 chirp, arising from the struggling prisoner within 

 the calcareous prison. At that period it has suc- 

 ceeded in penetrating through the little mem- 

 brane stretched across the air-sac, and it is now 

 enabled to breathe the air contained in it. Under 

 ordinary circumstances, where no covering has 

 been put upon the egg, the porous nature of the 

 shell must undoubtedly contribute to the renewal 

 of this little volume of air, which is too small to 

 supply the wants of the chick for any lengthened 

 time. From this time forward the chick is an air- 

 breathing creature; and, in the case of volant 

 birds, is soon to be issued into the world where 

 its sportings in that element will form a chief 

 occupation of its existence. 



The most interesting period in the life of the 



