26 



THE YOUNG NATURALIST. 



this bird could fly, its reptilian tail would not be so effective a rudder as that 

 of any of our existing birds ; and it is obvious that any tendency towards the 

 coalescence of the last caudal vertebrae and the consequent development of a 

 coccygean bone would give to its possessor an immense advantage in the 

 struggle for existence, and on the principle of the survival of the fittest and 

 the multiplication of those individuals possessing any special advantage, we 

 can easily see why all existing birds possess this remarkable development, 

 which furnishes them with such an effective steering apparatus. 



Of the other extinct toothed birds, the genus Ickthyornw comprising two 

 species, were small birds closely resembling the modem terns. The other 

 order, Hesperornis, were incapable of flight, had large bones, a long neck, 

 measured about 6 ft. over all and probably resembled our modern penguins. 



When once the evolutionary forces, whose effects we have endeavoured to 

 describe, had produced a true feathered bird, it is easy to see that the power 

 of flight would be of immense advantage to its possessor in enabling it not 

 only to escape its foes, but also to obtain a greater quantity and increased 

 variety of food. The constant use of the wings would, in a few generations, 

 tend to increase their size and their value to their owners. While land and 

 sea were alike overrun by gigantic reptiles, any tendency towards develop- 

 ment of increased walking and swimming powers would have been disadvan- 

 tageous, and consequently we find no trace during the Secondary period of 

 such birds as our present ostriches or their allies. The only direction in 

 which persistent variation could take place, was that of increased power of 

 flight, so that we can safely say that all existing birds are descended from 

 flying ancestors. After the close of the Secondary period, and the disappear- 

 ance of most of the great Saurians, there were in many parts of the world 

 places where modifications which were previously impossible or disadvantag- 

 eous might take place freely and persistently. We can well imagine the 

 ancestors of the ostriches, for instance, settling in some parts of Africa, where 

 as yet the Carnivora had not any sway. Being able to procure food without 

 the exertion of flight, and having no enemies, disuse would rapidly diminish 

 the size of the wings, whilst simultaneously the greater use of the legs would, 

 in a few generations increase their size. When once the power of flight was 

 lost and the struggle for existence became more severe, owing to the presence of 

 the Carnivora, we find them gaining great strength and speed, so much so, that 

 they are able to hold then own even against the king of beasts. Again, we 

 see another line of adaptation to surroundings, in the auks and penguins, who 

 in their island homes, have little fear of molestation, and so we find the wings 

 absolutely useless for flight, but as fins very useful in their semi-aquatic life. 

 These birds mo Ye very awkwardly on land, hobbling in an extremely ludicrous 



