CHAPTER II 



Environment, Past and Present 



In the popular mind one of the chief distinctions 

 between plants and animals is that the former are 

 fixed, the latter capable of free movement. And 

 this is roughly true in spite of exceptions both ways. 

 It is natural that among the smaller forms of animal 

 life movements should be more or less curtailed for 

 limitations of size may be as effective as limitations 

 of organization. The microscopic Paramecium 

 which flashes across the field of the microscope 

 apparently at the speed of a greyhound, actually 

 travels only a few feet an hour but could it be en- 

 larged to the size of a horse and retain its own speed 

 in proportion, it would travel as fast as a horse in 

 full gallop. Its tie is diminutive size, not lack of 

 ability. There are, on the other hand, such beasts 

 as the giant cuttlefishes that may weigh nearly three 

 tons but yet ''get nowhere." They have size, not 

 speed; organization is as important as bulk. 

 Given both size and equipment, other limits may yet 

 be imposed on distribution. Thus a terrestrial ani- 

 mal, no matter how large or how speedy, constantly 

 confronted with barriers, cannot hope to compete 



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