6 4 



air supply used by persons descending foul mines, etc., is stored. If a 

 long continued blast occurs, wbile tbe bird is flying, the difficulty of 

 filling the lungs then would be very great, whereas sufficient could be 

 drawn from the reservoirs to tide over the gush and the supply could be 

 renewed as soon as the break in the wind occurred. This theory 

 practically embodies Theory No. 3, except that in my suggestion the supply 

 is not in constant use, but is only drawn on in case of need. 



Mr. Miiller discredits the respirator}' function theory very ably by 

 showing that " at each inspiration the air would give off some of its 

 oxygen in the lungs but not in the air sacs. At the expiration that air from 

 the lungs would pass through the bronchi into the trachea and the air from 

 two air sacs would pass into the lungs and there be deprived of some of its 

 oxygen. At the next inspiration the air in the lungs (poor in oxygen) 

 would be driven back into air sacs. At the next inspiration the air from 

 the air sacs would pass again into the lungs and being poor in oxygen 

 would be ill adapted for respiratory purposes." The process continued 

 would of course result in the air sacs being in time practically deprived 

 of all its oxygen. 



Now, just for the sake of argument, take it that my theory is feasible. 

 The bird starts off with a good supply of air, both in the lungs and in the 

 air sacs. Circumstances arise which necessitate the bird drawing upon its 

 reserve air. The lungs are filled with an internal inspiration, so to speak, 

 and the expiration, which would necessarily follow, would leave both air 

 sacs and lungs practically empty. Now supposing the air sacs have a 

 physiological function, the following inspiration would fill the air sacs 

 and the lungs with anew supply and the bird is ready to encounter a pro- 

 longed gust of wind or whatever circumstances that might entail its 

 existing for a longer period without an external inspiration than usual. 



Apart from the reservoir theory however. To my mind the following 

 process might quite reasonably be expected to take place. The first inspira- 

 tion fills the lungs and the air sacs; then follows the expiration. The air 

 passing from the air sacs to the lungs counts as the next inspiration, as I 

 term it an internal inspiration. What naturally follows is an expiration of 

 the air already in the lungs and not as one would he led to suppose from 

 Mr. Miiller's theory, an inspiration leaving both lungs and air sacs ready for 

 a new supply altogether. I may of course be arguing upon a perfectly 

 wrong basis, and the bird may not be able to fill the air sacs ; but if it is 

 able to do this, it seems unnatural that there should be two inspirations to 

 one expiration. I quote at the end of this article, verbatim, Mr. Miiller's 

 theory taken from The Field, of March 28th, from which my line of argu- 

 ment will perhaps be more clear. 



Now take another discredited theory, No. 4. What is the reason of 

 the curious up and down flights of such birds as the Goldfinch. At the first 

 pulse of the bird's wings, the bird rises, at the top of the pulse the highest 



