124 THE BRITISH NATURALIST. [June 



tail as a more effective rudder or steering apparatus, would tend to be 

 preserved and accentuated because of the increased power it would 

 give, of escaping foes as well as obtaining greater quantity and variety 

 of food. It is not likely, that during the secondary period when sea 

 and land were over-run with enormous reptiles, any development of 

 leg power such as we see in the ostriches would take place, and it is 

 probable that the power of flight would be still further specialized, | 

 since birds only possessing small flying power and inefficient steering 

 apparatus would fall easy victims to the Pterosaurians, which exercised a 

 reign of terror in the air, as did the Dinosauvians on the land. This 

 justifies the assertion, supported by other anatomical considerations, 

 that all existing birds are descended from flying ancestors, and that 

 forms so different as the Penguin and the Ostrich, are simply 

 specializations for marine and terrestial life. The development of the 

 coccygean bone is intimately associated with that of the power of | 

 flight. All existing birds which are strong on the wing (with one | 

 group of exceptions) are remarkable for the large ploughshare bone | 

 which supports the tail feathers. The exceptions are a few of the ; 

 long-legged birds such as Herons, Cranes, Spoonbills, and Flamingoes, | 

 which fly with their legs stretched out behind them, using them as | 

 rudders and consequently in these birds the coccyx is very small, i 

 In Apteryx and the Penguin, the Cassowary and Emu, the coccygean | 

 bone is not ploughshare shaped but rod-like ; still, it is evidently I 

 formed by the fusion of several of the terminal caudal vertebrae. As j 

 these birds never fly, this is only what might be expected. In the I 

 Ostrich, the shape of the coccyx is more like that of the flying birds, i 

 but in Rhea sometimes called the American Ostrich, it would seem 



i. 



that we have either a reversion to an earlier type or a descendant of 

 an order of birds which had never developed the coccygean bone, j 

 since Rhea does not possess one, its short tail being as distinctly | 

 reptilian in shape as that of Archaeopteryx. - | 



It may be asked, is not this inconsistant with what has been . 

 already said as to all existing birds being decendants of flying 

 ancestors. An examination of the wing-bones of the Rhea at once 



settles this question ; though slender they are very much longer than 1 1 



those of any other running bird, and the absence of the coccyx cannot i) 



out-weigh the other evidence that Rhea is descended from a flying j: 



ancestor. The same holds good of the other running birds; j' 



