The Geographical Distribution of Fishes 97 
current, bearing Ochotsk-Alaskan types southward as far as 
the Santa Barbara Islands, to which region it is accompanied 
by species of Aleutian origin. A cold return current seems to 
extend southward in Japan, along the east shore perhaps as 
far as Matsushima. A similar current in the sea to the west of 
Japan extends still further to the southward, to Noto, or beyond. 
It is, of course, not necessary that the movements of a 
species in an oceanic current should coincide with the direction 
of the current. Young fishes, or fresh-water fishes, would be 
borne along with the water. Those that dwell within floating 
bodies of seaweed would go whither the waters carry the drift- 
ing mass. But free-swimming fishes, as the mackerel or flying- 
fishes, might as readily choose the reverse direction. Toa free- 
swimming fish the temperature of the water would be the only 
consideration. It is thus evident that a current which to certain 
forms would prove a barrier to distribution, to others would be 
a mere convenience in movement. 
In comparing the Japanese fauna with that of Australia, we 
find some trace of both these conditions. Certain forms are 
perhaps excluded by cross-currents, while certain others seem 
to have been influenced only by the warmth of the water. <A 
few Australian types on the coast of Chile seem to have been 
carried over by the cross-currents of the South Atlantic. 
It is fair to say that the part taken by oceanic currents in 
the distribution of shore fishes is far from completely demon- 
strated. The evidence that they assist in such distribution 
is, in brief, as follows: 
1. The young of shore fishes often swim at the surface. 
2. The young of very many tropical fishes drift northward 
in the Gulf Stream and the Japanese Kuro Shiwo. 
3. The faunal isolation of Hawaii may be correlated with 
the direction of the oceanic currents. 
Centers of Distribution.—We may assume, in regard to any 
species, that it has had its origin in or near that region in which 
it is most abundant and characteristic. Such an assumption 
must involve a very large percentage of error or of doubt, but 
in considering the mass of species, it may represent essential 
truth. In the same fashion we may regard a genus as being 
autochthonous or first developed in the region where it shows 
