THE DISTRIBUTION OF ANIMALS. 363 
while those near the Atlantic coast are more like those of 
Asia. Not half a dozen Insects live in the sea. 
The distribution of Fishes is bounded by narrower lim- 
its 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 Geol- 
ogy. 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 no 
Batrachians, and two-thirds of its Snakes are venomous. 
In the United States, only 22 out of 176 are venomons. 
Frogs, Snakes, and Lizards occur at elevations of over 
15,000 feet. Crocodiles, and most Lizards and Turtles, 
are tropical. 
Swimming Birds, which constitute about one-fourteenth 
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. In- 
dia and South America are the richest regions. Birds 
with rudimentary wings, as Penguins and Ostriches, pre- 
vail in the southern hemisphere. Hummers, Tanagers, 
Orioles, and Toucans are restricted to the New World. 
Parrots are found in every continent, except Europe; and 
Woodpeckers occur everywhere, save in Australia. 
The vast majority of Mammals are terrestrial; but Ce- 
taceans and Seals take to the sea, Otters and Beavers de- 
