V/7 



PREFACE. 



IN almost every large group of animal life there is a 

 curious tendency towards usurping the domain which 

 is usually occupied by other groups. 



Taking, for example, the Fishes as typical occu- 

 piers of the water, we find that there are various 

 groups of Mammalia, Birds, Reptiles, Insects, etc., 

 which live almost as much in the water as do the 

 Fishes themselves. Such, for example, are the 

 Whales and Dolphins among the Mammalia, the 

 Penguins among the Birds, the Turtles, Water Snakes 

 and Newts among the Reptiles, and the Water Beetles 

 among the Insects. 



Then, we have the Bats as examples of mammalia 

 which trespass on the domain of the birds j while the 

 Flying Monkey or Colugo, the Flying Squirrels of 

 the Old World, and the Flying Phalangists of Aus- 

 tralasia, are examples of partial Trespassers in the 

 same direction. With regard to reptiles (putting 

 aside the extinct Pterodactyls) we have the Flying 



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