334 



MORRIS M. WELLS, 



be less resistant per individual than smaller fishes of the same 

 species. That such is the case with the rock bass is indicated 

 in the table. 



Now if this relation holds in general, the expectation would 

 be, that young fishes of a large species will possess greater powers 

 of resistance than adult fishes of another but smaller species, 

 when the young of the larger and the adults of the smaller species 

 are of the same weight. That such an assumption is tenable is 

 illustrated by nearly all the experiments in which such young and 

 adults occurred. For purpose of illustration, a table showing 

 the results of a series of such experiments is inserted. 



Of the species occurring in Table III. the darters and the 

 shiner are small, seldom weighing more than 2 or 3 grams. The 

 red horse is a large species but is easily killed by slight changes 

 in the content of the water (Forbes and Richardson '08, p. 91). 

 Adults of the remaining three species are rather large and 

 resistant. 



TABLE III. 



SHOWING THE RESISTANCE OF SMALL FISHES TO Low OXYGEN (.i-.is c.c. PER 

 LITER) AND Low CARBON DIOXIDE (i c.c. PER LITER). 



A glance at the table will show r that although the young of 

 the rock bass, the river chub, and the common shiner, weighed 

 less than the darters, and only in the case of the rock bass more 

 than the shiner (Notropis atherinoides] , still they proved to be 

 more resistant than the adult darters and shiners, by a con- 

 siderable margin. 



Because of the fact that there was often a break in the in- 

 creasing weights of the fishes used, and because it was found to 

 be hardly possible to compare species one with another, if the 



