282 C. H. HURST, PH.D. 



relation with air capable of far more rapid renewal than in the 

 mammalian lung. In other words, birds breathe the tidal air, while 

 mammals breathe the residual air. Archceopteryx, however, shows no 

 sign of the possession of large air-sacs, or of that large expanded 

 sternum which, in modern birds of flight, insures the rapid change of 

 the air by the same muscular movements as are involved in flight 

 itself. While in all powerful fliers, both birds and insects, every 

 movement of the wing insures a change of the air in the respiratory 

 organ itself (and not merely in the passages leading to that organ), 

 the form and structure of Archceopteryx forbid us to believe that such 

 an adaptation existed in it. 



Conclusions as to the size and efficiency of the heart might be 

 drawn, but they are not only obvious but also perhaps a little risky ; 

 so I will leave them. 



Nobody, except the constructors of flying-machines, seems to be 

 ignorant of the fact that all powerful fliers have a wing-area which is 

 very large in proportion to the area of the immoveable aeroplanes. 

 Birds do not nowadays rely upon immoveable aeroplanes at all. The 

 wings serve all the functions of both propulsion and sustentation, and 

 the tail when used at all is used only for steering ; while the vastly 

 superior flight of insects is effected in the absence of any special 

 steering apparatus, the wings themselves serving alike for propulsion, 

 sustentation, and steering. 



In Archceopteryx, then, we find an animal as yet not evolved beyond 

 the aeroplane phase of flight ; a phase characterised by the use of 

 large aeroplanes, which, while offering considerable resistance to flight, 

 take no part in the propulsion. It may further be pointed out that 

 among flying things, whether birds, mammals, insects, or flying 

 machines, the most efficient are all far broader from side to side than 

 they are long. Lilienthal, alone among men who seek to fly, seems to 

 have appreciated the real bearing of this fact. The further mechanical 

 consideration of the point, even as applied to Archceopteryx, would, 

 however, take us too far. It is sufficient for my present purpose to 

 have pointed out wide differences of structure both as to the imme- 

 diate organs of flight and also as to the propelling muscles and the 

 respiratory organs on which powerful flight depends, between, on the 

 one hand, Archceopteryx, and, on the other hand, all other flying 



