DISTRIBUTION OF THE FAUNAS. 205 



and variety elsewhere unknown ; and lastly, the Polyps there 

 display an activity of which the other zones present no ex- 

 " ample. Whole groups of islands are surrounded with coral 

 reefs formed by those little animals. 



435. The variety of the tropical fauna is further enriched 

 by the circumstance that each continent furnishes new and 

 peculiar forms. Sometimes whole types are limited to one 

 continent, as the sloth, the toucans, and the humming-birds to 

 America, the giraffe and hippopotamus to Africa ; and again 

 animals of the same group have different characteristics, ac- 

 cording as they are found on different continents. Thus, 

 the monkeys of America have flat and widely separated 

 nostrils, thirty-six teeth, and generally a long, prehensile tail. 

 The monkeys of the Old World, on the contrary, have nostrils 

 close together, only thirty-two teeth, and not one of them has 

 a prehensile tail. 



436. But these differences, however important they may 

 appear at first glance, are subordinate to more important 

 characters, which establish a certain general affinity between 

 all the faunas of the tropics. Such, for example, is the fact 

 that the quadrumana are limited, on all the continents, to 

 the warmest regions ; and never, or but rarely, penetrate 

 into the temperate zone. This limitation is a natural con- 

 sequence of the distribution of the palms ; for as these trees, 

 which constitute the ruling feature of the flora of the tropics, 

 furnish, to a great extent, the food of the monkeys on both 

 continents, we have only to trace the limits of the palms, to 

 have a pretty accurate indication of the extent of the tropical 

 faunas on all three continents. 



437. Several well-marked faunas may be distinguished in 

 the tropical part of the American continent, namely : 



1. The fauna of Brazil, characterized by its gigantic rep- 

 tiles, its monkeys, its Edentata, its tapir, its humming-birds, 

 and its astonishing variety of insects. 



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