372 COMPARATIVE ZOOLOGY. 



"Great fleas have little fleas and smaller fleas to bite 'em ; 

 And these again have other fleas, and so ad infinitum." 



Thus the ocean of life is inexhaustible. It spreads in 

 every direction, into time past and present, flowing every- 

 where, eagerly surging into every nook and corner of cre- 

 ation. On the mountain-top, in the abysses of the Atlan- 

 tic, in the deepest crevice of the earth's crust, we tind 

 traces of animal life. Nature is prodigal of space, but 

 economical in filling it. 190 



Animals are distributed over the globe according to 

 definite laws, and with remarkable regularity. 



Each of the three great provinces, Earth, Air, and Wa- 

 ter, as also every continent, contains representatives of all 

 the classes ; but the various classes are unequally repre- 

 sented. Every great climatal region contains some species 

 not found elsewhere, to the exclusion of some other forms. 

 Every grand division of the globe, whether of land or 

 sea, each zone of climate and altitude, has its own fauna. 

 And, in spite of the many causes tending to disperse ani- 

 mals beyond their natural limits, each country preserves 

 its peculiar zoological physiognomy. 



The space occupied by the diiferent groups of animals 

 is often inversely as the size of the individuals. Compare 

 the Coral and Elephant. 



The fauna now occupying a separate area is closely al- 

 lied to the fauna which existed in former geologic times. 

 Thus, Australia has always been the home of Marsupials, 

 and South America of Edentates. 



It is a general rule that groups of distinct species are 

 circumscribed within definite, and often narrow, limits. 

 Man is the only cosmopolitan ; yet even he comprises sev- 

 eral marked races, whose distribution corresponds with the 

 great zoological regions. The natives of Australia are as 

 grotesque as the animals. Certain brutes likewise have a 

 great range : thus, the Puma ranges from Canada to Pata- 



