Insecta. 17 



thickened, as in its situation covers are not needed. It 

 should have wings constantly poised, ready to dart in- 

 stantly after its prey. There is no objection to having the 

 wings continually spread, as it lives in open spaces and 

 does not have to crawl through grass and twigs ; and the 

 increased area due to the spread does not especially endan- 

 ger it by making it more conspicuous, since it has compara- 

 tively few enemies. The body is too heavy, and it must 

 " train down " until it can handle itself better. The legs 

 are too heavy, especially the hind pair ; and, as it uses them 

 very little except to perch upon a leaf or twig, waiting for 

 something to turn up, this matter takes care of itself, for 

 any unused organ is likely to dwindle away. 



It needs keener eyes, for it no longer feeds on plants 

 which are sure to stay in place while it crawls upon them ; 

 it is another matter to discern small insects at some dis- 

 tance. So it develops better eye power to discover its food, 

 as well as better wing power to overtake it after seeing it. 

 It had fairly good jaws before, but they become some- 

 what enlarged and better adapted to the new work. The 

 enlargement of the jaws and the eyes make the whole 

 head bigger than it was before. 



Of course insects do not trade places in this manner; 

 nor does any insect suddenly change its habits. But we 

 can easily imagine that these two forms have descended 

 from the same ancestors and have gradually grown dif- 

 erent, each becoming fitted for the situation in which it is 

 placed. 



It is no longer supposed that all the forms of life we 

 now see on the earth have been distinct from the begin- 

 ning, for we see evidences that many forms have arisen 

 by the increase in numbers which establishes competition, 

 and which in turn has compelled dispersion and forced 



