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UNIVERSITY OF WISCONSIN STUDIES 



importance of means for dispersal and isolation are shown by 

 the fact that there are no frogs or snakes on Isla del Euro while 

 another island (Culebra) in the lake is so heavily infested with 

 poisonous snakes that the natives avoid it. 



In order to gain some idea of general conditions in Lake 

 Valencia a few limnological observations were made. Table I 



FIG. 2. Shore of Isla del Euro and tishing crew. 



TABLE I 



Temperature and gases (determined by the Winkler method) at various 

 depths in Lake Valencia July 17, 1918. Gases are given in c.c. per liter at 

 indicates that the water was alkaline as judged by phenapthaline titration 



with -TJQ sulphuric acid solution. The depth of the water where samples were 

 taken was 26 m. 



