104 The Geographical Distribution of Fishes 
basins of China and the Eastern United States, as compared with 
those of Europe or the Californian region. 
Minor divisions are those which separate the Great Lake 
region from the streams tributary to the Gulf of Mexico; and 
in Asia, those which separate China from tributaries of the 
Caspian, the Black, and the Mediterranean. 
Equatorial Zone.—The Equatorial Zone is roughly indicated 
by the tropics of Cancer and Capricorn. Its essential feature 
is that of the temperature, and the peculiarities of its divisions 
are caused by barriers of sea or mountains. 
Dr. Gunther finds the best line of separation into two 
divisions to lie in the presence or absence of the great group 
of dace or minnows,* to which nearly half of the species of fresh- 
water fishes the world over belong. The entire group, now 
spread everywhere except in the Arctic, South America, Aus- 
tralia, and the islands of the Pacific, seems to have had its 
origin in India, from which region its genera have radiated in 
every direction. 
The Cyprinoid division of the Equatorial Zone forms two 
districts, the Indian and the African. The Acyprinoid division 
includes South America, south of Mexico, and all the islands of 
the tropical Pacific lying to the east of Wallace’s line. This 
line, separating Borneo from Celebes and Bali from Lompoe, 
marks in the Pacific the western limit of Cyprinoid fishes, as 
well as that of monkeys and other important groups of land 
animals. This line, recognized as very important in the distribu- 
tion of land animals, coincides in general with the ocean current 
between Celebes and Papua, which is one of the sources of the 
Kuro Shiwo, 
In Australia, Hawaii, and Polynesia generally, the fresh- 
water fishes are derived from marine types by modification of 
one sort or another. In no case, so far as I know, in any island 
to the eastward of Borneo, is found any species derived from 
fresh-water families of either the Eastern or the Western Conti- 
nent. Ofcourse, minor subdivisions in these districts are formed 
by the contour lines of river basins. The fishes of the Nile differ 
from those of the Niger or the Congo, or of the streams of Mada- 
* Cyprinidae. 
