448 COMPARATIVE ZOOLOGY 



of Europe, while those near the Atlantic coast are more 

 like those of Asia. Less than a score of insects are 

 known to live in the sea. 



The distribution of fishes 'is bounded by narrower 

 limits than that of other animals. A few tribes may be 

 called cosmopolitan, as the sharks and herrings ; but 

 the species are local. Size does not appear to bear any 

 relation to latitude. The marine forms are three times 

 as numerous as the fresh-water. The migratory fishes of 

 the northern hemisphere pass to a more southern region 

 in the spring, while birds migrate in the autumn. 



Living reptiles form but a fragment of the immense 

 number which prevailed in the Middle Ages of geology. 

 Being less under the influence of man, they have not 

 been forced from their original habitats. None are 

 arctic. America is the most favored spot for frogs and 

 salamanders, and India for snakes. Australia has few 

 batrachians, and two thirds of its snakes are venomous. 

 In the United States, only about one eighth of the species 

 are venomous. Frogs, snakes, and lizards occur at ele- 

 vations of over fifteen thousand feet. Crocodiles, and 

 most lizards and turtles, are tropical. 



Swimming birds, which constitute about one four- 

 teenth of the entire class, form one half of the whole 

 number in Greenland. As we approach the tropics, the 

 variety and number of land birds increase. Those of 

 the torrid zone are noted for their brilliant plumage, 

 and the temperate forms for their more sober hues, but 

 sweeter voices. India and South America are the 

 richest regions. Hummers, tanagers, orioles, and tou- 

 cans are restricted to the New World. Parrots are 

 found in every continent except Europe; and wood- 

 peckers occur in every region, save in Australia. 



The vast majority of mammals are terrestrial; but 

 cetaceans and seals belong to the sea, otters and beavers 



