36 A BOOK OF INSECTS 



" struggle for existence " which goes on among all living 

 things, and of the " survival of the fittest." 



There is much in the lives of insects that will cause us 

 to ponder this law of natural selection, and we shall do 

 well to grasp its exact import. Little evidence exists 

 to support the view that characteristics acquired during 

 the life-spell of an individual, as distinct from those which 

 come to it as the result of inborn (or congenital) variation, 

 are transmitted from parent to offspring. " On this view " 

 (says Professor Carpenter) " the broad fore-limbs of earth- 

 burrowing insects like the mole-cricket are the direct 

 result of a digging habit persevered in through many- 

 generations, while the wingless condition of many female 

 and parasitic insects is simply due to their ancestors 

 having given up flying. It is hardly necessary to point 

 out how differently the natural selection theory accounts 

 for such facts as these. According to its advocates no 

 amount of the most vigorous digging on the part of a 

 primitive cricket would avail to provide its descendants 

 with broad fore-legs; these organs are believed to have 

 been slowly specialised through a long series of genera- 

 tions of crickets, which were adopting the burrowing 

 habit, through the selection in each generation of those 

 individuals best adapted for burrowing, that is, those 

 which possessed the broadest and strongest fore-legs, the 

 broadening not being an acquired but a congenital 

 character. And there is no doubt whatever that con- 

 genital characters are transmissible. In the same way it 

 would be believed that the loss of wings in the insects 

 mentioned above being, for some reason, actually bene- 

 ficial to the species, individuals with the smallest wings 

 were selected through numerous generations until those 

 organs were almost or entirely lost." 



We must not suppose, however, that the perpetuation 



