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 2 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 Lucifuga and Stygicola, fishes allied to the Cod, and belonging 
to the family of Broteulide. 
2 Amblyopsis, Typhlichthys. 
3 Lepisosteus tristachus. 
