October 11, 1901.] 



SCIENCE. 



561 



The westward current from Hawaii 

 reaches Luzon and Formosa. It is deflected 

 to the northward and, joining a northward 

 current from Celebes, it forms the Kuro 

 Shiwo or Black Stream of Japan, which 

 strews its tropical species in the rock pools 

 along the Japanese promontories as far as 

 Tokio. Then, turning into the open sea, it 

 passes northward to the Aleutian Islands, 

 across to Sitka. Thence it moves south- 

 ward as a cold current, bearing Ochotsk- 

 Alaskan types southward as far as the Santa 

 Barbara Islands, to which region it is fol- 

 lowed by species of Aleutian origin. A 

 cold return current seems to extend south- 

 ward in Japan, along the East shore per- 

 haps as far as Matsushima. A similar cur- 

 rent 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 cur- 

 rent 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 drifting mass. But free-swimming 

 fishes, as the mackerel or flying-fishes, 

 might as readily choose the reverse 

 direction. To a 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 

 excluded by cross-currents, while certain 

 others seem to have been influenced only 

 by the warmth of the water. A few Aus- 

 tralian types on the coast of Chili seem to 

 have been carried over by the cross currents 

 of the South Atlantic. 



CENTERS OF DISTRIBUTION. 



We may assume, in regard to any spe- 

 cies, 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 certain percentage of error or of 

 doubt, but in considering the mass of spe- 

 cies, it would represent essential truth. In 

 the same fashion, we may regard a genus 

 as being autochthonous or first developed in 

 the region where it shows the greatest range 

 or variety of species. Those regions where 

 the greatest number of genera are thus au- 

 tochthonous may be regarded as centers of 

 distribution. So far as the marine fishes 

 are concerned, the most important of these 

 centers are found in the Pacific Ocean. 

 First of these in importance is the East-In- 

 dian Archipelago, with the neighboring 

 shores of India. Next would come the 

 Arctic Pacific and its bounding islands, 

 from Japan to British Columbia. Third in 

 importance in this regard is Australia. Im- 

 portant centers are also found in temperate 

 Japan, in California, the Panama region, 

 and in New Zealand, Chili and Patagonia. 

 The fauna of Polynesia is almost entirely de- 

 rived from the Indies ; and the shore-fauna 

 of the Eed Sea, the Bay of Bengal and 

 Madagascar, so far as genera are concerned, 

 seems to be not really separable from the 

 Indian fauna generally. 



I know of but six genera which may 

 be regarded as autochthonous in the Red 

 Sea, and nearly of these are of doubtful 

 value or of uncertain relation. The many 

 peculiar genera described by Dr. Alcock, 

 from the dredgings of the Investigator in 

 the Bay of Bengal, belong to the bathybial 

 or deep water series, and will all, doubt- 

 less, prove to be forms of wide distribution. 



In the Atlantic, the chief center of dis- 

 tribution is the West Indies ; the second is 

 the Mediterranean. On the shores to the 

 northward or southward of these regions 

 occasional genera have found their origin. 



