CHAPTER XV. 



ISTHMUS BARRIERS SEPARATING FISH FAUNAS 



HE Isthmus of Suez.— In the study of the effect of the 

 Isthmus of Suez on the distribution of fishes we 

 may first consider the alleged resemblance between 

 the fauna of the Mediterranean and that of Japan. Dr. 

 Gunther claims that the actual identity of genera and species 

 in these two regions is such as to necessitate the hypothesis 

 that they have been in recent times joined by a continuous 

 shore-line. This shore-line, according to Prof. A. E, Ortmann 

 and others, was not across the Isthmus of Suez, but farther 

 to the northward, probably across Siberia. 



The Fish Fauna of Japan. — For a better understanding of 

 the problem we may give a brief analysis of the fish fauna of 

 Japan. 



The group of islands which constitute the empire of Japan 

 is remarkable for the richness of its animal life. Its variety in 

 climatic and other conditions, its nearness to the great con- 

 tinent of Asia and to the chief center of marine life, the East 

 Indian Islands, its relation to the warm Black Current or Kuro 

 Shiwo from the south and to the cold currents from the north, 

 all tend to give variety and richness to the fauna of its seas. 

 Especially is this true in the group of fishes. In spite of the 

 political isolation of the Japanese Empire, this fact has been 

 long recognized and the characteristic types of Japanese fishes 

 have been well known to naturalists. 



At present about 900 species of fishes are known from the four 

 great islands which constitute Japan proper — Hondo, Hokkaido, 

 Kiusiu, and Shikoku. About 200 others are known from the 

 volcanic islands to the north and south. Of these 11 00 species, 

 about fifty belong to the fresh waters. These are all closely 

 allied to forms found on the mainland of Asia, from which re- 



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