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PROBLEMS OF BIRD LIFE. 



Vertebrate Animals. 



By writing an answer to each question and reading the 

 columns downward, he will make a definition of each class of 

 creatures. Try this yourself and see how well you succeed. 

 At least you will find ' yourself giving definitions very differ- 

 ent from those you would have given a few minutes before. I 

 suspect that had you been asked what a fish is, you would 

 have said, "A fish is a swimming creature," and you would 

 have defined a tod as "a creature that flies." Then what a 

 tangle we should have been in ! There are birds that swim 

 nearly all the time, and mammals that cannot live out of 

 water, reptiles that swim as well as fishes, and fishes that 

 come out on/ dry land. And there are lizards that fly, and 

 reptiles that fly, and mammals that fly, not perhaps as well 

 as most birds, but much better than some birds, which do not 

 fly at all. 



You see now the difference between a scientific definition 

 and an unscientific one. The scientific definition refers to one 

 thing or class of things and to nothing else. It is accurate. 

 You have seen how scientific definitions are made; indeed, 



