126 SCIENCE SKETCHES. 



of these are evidently indigenous, derived in the 

 waters they now inhabit directly from marine 

 forms. Two of these are eyeless species,^ inhabit- 

 ing streams in the caverns. They have no rela- 

 tives in the fresh waters of any other region, the 

 Blind-fishes ^ of our caves being of a wholly dif- 

 ferent type. Some of the Cuban fishes are com- 

 mon to the fresh waters of the other West Indies. 

 Of Northern types, only one, the Alligator Gar,^ 

 is found in Cuba, and this is evidently a filibuster 

 immigrant from the coasts of Florida. 



The low and irregular water-shed which sepa- 

 rates the tributaries of Lake Michigan and Lake 

 Erie from those of the Ohio is of little importance 

 in determining the range of species. Many of the 

 distinctively Northern fishes are found in the head- 

 waters of the Wabash and the Scioto. The con- 

 siderable difference in the general fauna of the 

 Ohio Valley as compared with that of the streams 

 of Michigan is due to the higher temperature of 

 the former region, rather than to any existing bar- 

 riers between the river and the Great Lakes. In 

 northern Indiana the water-shed is often swampy, 

 and in many places large ponds exist in the early 

 spring. 



At times of heavy rains many species will move 

 through considerable distances by means of tem- 

 porary ponds and brooks. Fishes that have thus 

 emigrated often reach places ordinarily inacces- 



1 Luciftiga 2iw6. Sfygicola, fishes allied to the Cod, and belonging 

 to the family of Brottilidce. 



2 Amblyopsis, Typhi ichthys. 

 ^ Lepisosteiis tristoechus. 



