CASES OF ADAPTATION" 16^ 



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size and beauty, the Lepidoptera, are first in Tertiary beds, 

 at a time when birds allied to living forms also first appeared. 

 This general parallelism of development seems clearly to 

 indicate that birds, in the full and varied perfection in which 

 we now find them, are dependent on a correspondingly wide- 

 spread development of insects ; and more especially of those 

 higher orders of insects, whose exceedingly diverse stages of 

 larva, pupa, and perfect insect, afforded the special food for 

 immature and full-grown birds respectively. We can see how 

 the omnipresence of insects adapted to feed on every kind of 

 vegetable food, as well as on all kinds of animal refuse, has 

 afforded sustenance to the various kinds of small mammalia, 

 reptiles, and birds, which have successively become specialised 

 to capture and feed on them. The early birds with toothed 

 jaws were able to feed upon the cockroaches and ancestral 

 iVTeuroptera and beetles of the same period. As these early, 

 birds became more numerous, so they became successively 

 specialised to feed upon particular kinds of insects or their 

 larvae, however completely these might seem to be concealed 

 or protected. Thus were gradually formed the true fly- 

 catchers (Muscicapidge) and the totally distinct American fly- 

 catchers or tyrant birds (Tyrannidse), which capture all kinds 

 of insects on the wing; the swallows, and the very distinct 

 swifts, so specialised as almost to live in the air, and to feed 

 on this kind of food exclusively; the goatsuckers, which 

 capture night-flying insects; the curious little nuthatches and 

 creepers which hunt over trees for small beetles concealed in 

 crevices of the bark; while the marvellously specialised wood- 

 peckers discover the larger grubs or caterpillars which burrow 

 deeply into the wood of trees, and dig down to them with 

 their wonderfully constructed hammer-and-chisel-like head 

 and bill, and then pull them out on the tip of their extensile 

 barbed tongue. In the tropics many distinct families of birds 

 have been developed to grapple with the larger and more 

 varied insect forms of those countries, so that it mav be 

 safely concluded that no group of the vast assemblage of in- 



