i89i.] 



THE BRITISH NATURALIST. 



125 



if it were not so, why have they all the bones of the iiying birds ? 

 identical bone for bone, though reduced in size, so much so that in 

 some they bear no wing-feathers. It is impossible that these wing bones 

 can be nascent since they are absolutely functionless. Whilst 

 speaking of the wing-bones it may be mentioned that they are 

 identical with those of the fore-limb of a reptile. When we examine 

 the wing bones of the Penguins and allied species, we find that they 

 are not materially reduced in size, since though in these birds the 

 power of flight is lost, the wings serve as swimming organs. 



We have seen that it was highly improbable that any persistent 

 variation in the direction of leg power, such as marks the existing 

 Ostriches, could take place in the secondary period, yet at the close of 

 that period after the disappearance of the great saurians there would be 

 many parts of the world in which modifications which were previously 

 disadvantageous might take place freely and persistently. Some of 

 these variations in the direction of lessened wing power, which owing 

 to the extreme severity of the struggle for existence, had not previously 

 been able to maintain themselves, would now become established and 

 intensified. The great Dinosaurians as well as the formidable flying 

 reptiles had become extinct, the large carnivora had not yet been 

 developed, and so birds of small wing power could grow and multiply. 

 It is certain that diminished wing power would be accompanied by 

 increased development in other directions, and so would be evolved 

 from the strong-winged flying bird of one age, the weak-winged but 

 long-legged and long-necked running bird of a later time. When 

 carnivora became numerous the struggle for existence would again 

 become intensified, and the smaller or less active running birds would 

 fall victims unless able to conceal themselves ; any favorable variation 

 in the direction of increased strength or speed would be preserved, and 

 just as accumulated variations had in an earlier age produced a flying 

 feathered bird from a scaly tree lizard, so from the running weak 

 winged descendants of flying birds were produced such giants as the 

 Asiatic ostrich of Tertiary times, as well as the ancestors of our 

 existing Rheas, Emus, and Cassowaries. It is difficult to conceive 

 any other explanaiion of the origin of the remarkable birds which 

 formerly existed in New Zealand. Of this group there were not less 

 than 18 species, some of which obtained a height of 16 ft. Amongst 

 these Moas, of course there were variations in size, but all, whether 



