292 THE LIFE OF A BIRD. 



this exquisite lace-work of blood-vessels is a simple 

 but beautiful and perfect substitute for the lungs. 

 The blood in these delicate tubes being brought 

 near to the external wall of the egg, it is supposed 

 that air passes in and out through the pores of the 

 shell, and that thus the renewal of the blood is 

 effected. Respiration is thus carried on until the 

 nineteenth day of incubation, when the lungs are 

 called into play. 



The receptacle of air at the large end of the egg 

 has been thought to serve a most important end in 

 this process. Dr. Paris, in a paper published YoL 

 X. of the Linnrean Transactions, carefully analysed 

 the air contained in this little sac. By perforating 

 twenty-one fresh-laid eggs at the large ends, and 

 collecting the gas in a jar which amounted to a 

 cubic inch, he found it to be pure atmospheric air. 

 Two eggs were opened after incubation had gone 

 on for some days, which yielded an inch of air. 

 On examination, some carbonic acid gas was found 

 in this air. Other observers have also analysed 

 the air contained in this receptacle. M. Bischoff 

 found it to contain more oxygen than atmospheric 

 air. M. Dulk arrived at the same conclusion, 

 and found after incubation, that the quantity of 



