236 ON THE ORIGIN OF PLIGHT. [Feb. 19, 



decidedly lower than in other birds on the one hand (Sutherland), 

 and their reduced brachiosternal muscles on the other (Fiirbringer), 

 can likewise be appreciated only if we consider them as forms 

 that specialised at a very early stage of Avian evolution. 



It is to be remarked that among the terresti-ial birds which 

 according to this hypothesis would seem to have preserved their 

 orio-inal mode of living and manner of breeding, the nest-building 

 faculty is less developed than in those birds which, to avoid 

 the dangers of ground-life, migrated up into the trees and had 

 then to shelter their eggs and young ones from the new chance 

 of falling to the ground. That ground-Hfe involves for a bird 

 more dangers than life on a tree, I think, is shown by the fa,ct 

 that the true ground-birds usually are protectively coloured, while 

 in the latter, even among Gallinaceous Birds, bright — one might 

 nearly say artistic — sexual characters are frequently developed. 



The supposition, that Biixls once possessed a patagium and only 

 afterwards developed feathers, I consider as devoid of foundation, 

 for apart from the impossibility of a marginal feather being 

 effective, when only attached to a flexible membrane, it is loss 

 and not development of hair and scales (= epidermal coverings) 

 that takes place in the Chiropterygian and Pterosaurian patagium. 

 Besides, I do not see any reason why a useful patagium, once 

 developed, should suddenly have stopped growing. 



The long tail in Archceopteryx can in no way be invoked in 

 fa,vour of a primitive arboreal stage of Birds, for a long tail not 

 •only characterises arboreal but also bipedal cursorial and saltatorial 

 forms. Thus we cannot find a single character in Archmopteryx that 

 would absolutely prove arboreal specialisation, while the develop- 

 ment of the cannon-bone alone is sufficient to show with certainty 

 that some of the direct ancestors of Archceopteryx had cursorial 



habits. 



Conclusion. 



From a consideration of the whole of the above remarks, we 

 •can, 1 believe, formulate the following statement : — 



While Pterosaurs and Bats origioiated independently from 

 quadrupedal arboreal forms in which both anterior ami posterior 

 •extremities, in consequence of the development of a patagiimn, 

 became primarily equally used for flight and in consequence equally 

 unfit for locomotion on the ground, Birds originated from bipedal 

 Dinosaur-like running forms in which the anterior extremities, on 

 account of flapping movements, gradually turned to loings tvithout 

 thereby affecting terrestrial locomotion. This is also the reason why 

 Birds became dominant over all the rest of their aerial rivals. 



In conclusion, I take pleasure in thanking once more all the 

 gentlemen that helped me to compile this paper, notably Dr. K. 

 Andersen, Mr. G. A. Boulenger, Dr. Forsyth Major, Mr. W. P. 

 Pycraft, and Dr. A. S. Woodward, at the British Museum of 

 iSTatural History. 



P. Z. S. 1906, pp. 759-1052 were published on April lltli, 1907. 



