328 ANIMAL DEFENCES 



kind, and were presumably vegetarian. The evolution of flying 

 insects made the realm of air a new food-producing territory, and 

 this may have been one of the factors helping to bring about the 

 evolution of Birds, Flying Reptiles (long since extinct), and Bats. 

 Be that as it may, the flying habit in recent birds and bats affords 

 a certain amount of protection, though the device is so ancient 

 that its efficacy in this respect has been largely discounted by the 

 appearance of rapacious types with powers of flight. Insects, the 

 oldest fliers, have naturally suffered most from this cause, for they 

 prey upon one another, and are mercilessly thinned out by birds 

 and bats. Birds, which come next in order of antiquity, prey 

 upon one another, and it would appear that bats, the youngest 

 (so far as our knowledge goes) of flying groups, enjoy the largest 

 share of protection from their power of progression through the 

 air. It would be rash to even conjecture why flying reptiles 

 should have become extinct. Perhaps the competition with birds 

 became too keen; at any rate the experiment turned out a failure, 

 though in justice to their class it should be remembered that birds 

 are probably of reptilian stock, which may therefore be said to 

 have made two series of attempts at flight, conducted on different 

 lines, and one of which has been crowned with success. 



Underground Animals. — We have now seen how certain 

 forms of life have withdrawn themselves from the keen com- 

 petition which takes place upon the surface of the ground, and 

 gained more or less protection, while at the same time improving 

 their chances of getting sufficient food, by adopting an arboreal 

 or an aerial habit. Another line has been struck out by creatures 

 which have taken to live entirely underground. The subterranean 

 parts of plants and the organic matter contained in earth have 

 offered food to vegetarian forms, and these again have led to the 

 evolution of carnivorous species suited for progression below the 

 surface of the soil. This way of life has proved of advantage to 

 many sorts of animal, since it affords protection as well as food. 



Among vegetarian forms of the kind may be more particularly 

 mentioned Earth-Worms, certain adult Insects {e.g. Mole-Crickets), 

 and many Insect larvse {e.g. Cockchafer Grubs). Among carni- 

 vorous forms most specialized in accordance with underground 

 habits are found members of widely -different groups. As to 

 Mammals, we have, for instance, the Moles, belonging to the 

 large and primitive order of Insectivora, and the Pouched-Mole 



