THE DISTRIBUTION OF ANIMALS 441 



Even the unicellular forms, Stylonychia, for example, 

 have been found to be infested with parasitic protozoans. 



Thus the ocean of life is inexhaustible. It spreads 

 in every direction, into time past and present, flowing 

 everywhere, eagerly surging into every nook and corner 

 of creation. On the mountain top, in the abysses of 

 the Atlantic, in the deepest crevice of the earth's crust, 

 we find traces of animal life. Nature is prodigal of 

 space, but economical in filling.it. 177 



Animals are distributed over the globe according to 

 definite laws, and with remarkable regularity. 



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

 Water, as also every continent, contains representatives 

 of all the classes ; but the various classes are unequally 

 represented. 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 alti- 

 tude, has its own fauna. In traveling over the earth 

 and settling in new regions man has been accompanied 

 by many animals which have established themselves 

 and thriven in the land of their adoption. For example, 

 the house, or " English," sparrow has been brought to 

 America, and the sparrow and rabbit to New Zealand. 

 Hence, it is necessary to distinguish between the native 

 or indigenous fauna, and the introduced fauna, the latter 

 depending upon human agency. In spite of the many 

 causes tending to disperse animals beyond their natural 

 limits, each country preserves its peculiar zoological 

 physiognomy. 



The space occupied by the different groups of ani- 

 mals is often inversely as the size of the individuals. 

 Compare the coral and elephant. 



The fauna now occupying a separate area is closely 

 allied to the fauna which existed in former geologic 



