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vil FLIGHT 261 
there are facts at our disposal which are full of mean- 
ing, and which in a rough and ready way settle the 
question. (1) Birds have large appetites and rapid 
digestions, a great proof of vigour. (2) In proportion 
to their size they give off from their lungs more car- 
bonic acid than other animals, and this means greater 
destruction of tissue, which implies a greater expendi- 
ture of energy. (3) Their temperature is exceptionally 
high, irrefragable evidence of the rate at which they 
live. (4) They are capable of as great rapidity of 
movement as mammals, and they tire less soon. 
This points to superior quality of muscles. 
Proportion of Wing Area to Weight in Large and 
Small Birds. 
This is a more difficult question than it might on 
first thoughts appear to be. One elementary cause 
of error may be disposed of at once: the doubling of 
the size of the bird will not mean the doubling of the 
length and breadth of the wings, for in that case the 
wing area would be quadrupled.t. This will explain 
the following figures: the comparative wing areas of 
a Herring Gull and a Great Tit are represented by 
541: 31, 2.¢., the Gull’s expanse of wing is rather more 
than eighteen times that of the Tit, whereas the length 
is less than six times as much.2 It is the areas, then, 
and not the lengths or breadths, that we must compare, 
1 See fig. 29. 
2 I take the areas from Pieter Harting, quoted by Marey 
(Animal Mechanism, p. 224), and the lengths from Howard 
Saunders’s Manual of British Birds. The results are too broad 
to be affected by differences in different specimens. 
