16 GEOGRAPHICAL DISTRIBUTION OF ANIMALS. 
















marine species,* passes just north of the Bermudas, and all 
the germs of tropical life that cross this line must perish. q 
The marine fauna of the West Indies extends to Bermuda, 
but, arrived at the Azores, the winter temperature has fallen. 
to less than 60° F., and we have the fauna of the Mediter- 
ranean and none of the characteristic Bermuda species. On 
the other hand, in the Pacific, where the equatorial current 
flows continuously within the isocrymals of 68° north and 68° — 
south, there are many species of mollusks, crustaceans, and | 
echinoderms found from the Sandwich Islands to the coast — 
of Africa, or through half the circumference of the globe. 
The mere intervening deep ocean, without connecting 
islands, might prevent the occurrence of some of the Ber- 
muda species at the Azores, as in the corals, the young of 
which probably cannot exist very long without becoming — 
attached; but even along continuous coast lines, very few 
species extend through marked changes of temperature. 
the western coast of America, a large part of the mollusks 
crustaceans, echinoderms, and some polyps, extend from 
Lower California to Guayaquil and a few to Paita, Peru, but 
very few species are common to Guayaquil and to Callao, — 
only a few hundred miles farther south. The isocrymals of 
62° to 68° F. all converge near Cape Blanco, and such 
change in temperature prevents the interchange of speci 
between places north and places south of this paints? 
The insular faunal character of the Americas has been re- 
marked by many naturalists, —most of the marine species of 
Ş 


the Crustacea, excluding the little known Entomostraca, Dana found, 
viel oremi na re faunal torrid zone and 924 in the temperate zone, only seventy 
mo two.—U. 8. Expl. Exp., Vol. XIII, p. 1527. As the range of 
becom por pean the pepara number of species common to the two zon 
will undoubts te ‘ increased, bu he fact is sufficient to show the great infiuence ! 


_ tMany of the Peruvian, and some Panamie species, are found at Paita, and mr 
blending does not 

a spain distance along the coast, and is what would ‘mp from the warm 
oe the colder. fedora are species which have their centre of greatest deve 
the border of a fauna it is nothing more than might 
th Sant 
intermediate between that of two faune. 

