RESISTANCE OF FISHES TO LACK OF OXYGEN. 443 



of more than one year's growth are included in it. The largest 

 specimen taken weighed 424 grams. 



It should be pointed out that not all the fishes collected were 

 easily classifiable into one or another of the above groups for 

 some were taken whose weights placed them on the border line 

 between two groups. This was especially true in the case of 

 groups two and three. However most of the fishes fell readily 

 into one of the five groups and only such fishes were used in the 

 experiments. 



III. EXPERIMENTAL METHODS. 



The resistance experiments were conducted as follows. A 

 starved fish from the experimental aquaria was placed in a large 

 (5-liter) wide-mouth bottle (low oxygen expt.) or in a battery jar 

 (KCN expt.) along with a control fish of the same group. The 

 control fish was selected so that its weight was very near the 

 original weight of the experimental fish. In most of the low 

 oxygen experiments a continuous stream of water flowed through 

 the bottle. This water came from an apparatus that removed 

 all but a trace of the oxygen. 1 The water flowed through the 

 bottle at the rate of 300 c.c. per min. 2 The solutions of KCN 

 were made up by diluting a standard N/ioo stock solution. The 

 battery jars were covered with glass plates during the experi- 

 ments. 



In all the experiments the control and the experimental fishes 

 were placed in the same bottle or jar. The caudal fin of the 

 control fish was clipped at the top and that of the experimental 

 fish at the bottom. The two were thus easily identifiable. 

 There was no evidence that the clipping of the fins had any effect 

 whatsoever upon the resistance of the fishes. All the control 

 fishes were collected just previous to the performing of the 

 experiments. 



IV. PRESENTATION OF DATA. 



i . Seasonal Resistance of the Fishes. 



During several years' collecting it had been noted that in 

 nature the resistance of fishes to detrimental factors in general, 



1 For description of apparatus see Shelford and Alice, 1913, p. 214. 



2 For complete description of methods of experimentation and recording, see 

 Wells, '13, pp. 325-29. 



