SIDE LIGHTS ON BIRDS 



follows the rapidly ascending form of the lark, 

 as it dwindles in size, rising higher and higher, or, 

 as he traces the course of the herring gull return- 

 ing seawards in the evening, its long, wide-spread 

 wings bearing it steadily onward with hardly a 

 perceptible beat : or, as he watches a company 

 of dunlin wheeling and turning in perfect unison, 

 their white underparts flashing in a momentary 

 burst of sunshine, only to sink once more into in- 

 visibility, swallowed up in a grey cloud back- 

 ground. 



Although all wings were originally made to fly 

 with, though a few have become diverted from 

 their original purpose, they are by no means all 

 made to one pattern. In form, colour, texture 

 and structure how many variations we see. Their 

 number alone remains constant : in vertebrates it 

 is invariably two ; in insects it is always either 

 two or four. Thus we may liken birds to mono- 

 planes, and butterflies to biplanes. The power 

 of flight is practically confined to the two classes, 

 birds and insects, and within these two orders, 

 it is a well-nigh universal accomplishment. 

 Still there are exceptions to this as to most rules. 

 For instance, bats fly, and ostriches can't; and 

 among the insects, grasshoppers, worker-ants, and 

 certain female moths are among those which, for 

 some reason or other, would seem to have been 

 unjustly deprived of their birth-right. Still the 

 great majority of insects have acquired mastery 

 of the air, and it is certain that no invertebrate 

 out of the insect class may ever aspire to do more 

 than crawl, swim, or wriggle through life. The 

 two great winged classes are for ever pitted against 

 one another in the struggle for existence, 

 and this, says Professor Arthur Thomson is 

 " practically the most important conflict of 

 classes the world knows." 



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