236 



VICTOR E. SHELFORD AND W. C. ALLEE 



marked preference for the low carbon dioxide, which was main- 

 tained for more than an hour. They showed no tendency toward 

 becoming accHmated to the carbon dioxide during this period. 



b. Reactions to oxygen 



In the experiments in which oxygen alone was varied, boiled 

 water was used at both ends and oxygen added at one end. 

 Titrations of collections from the ends of the tank showed a 

 gradient of 4 to 10 cc. per liter^ but as has already been stated, 

 these collections tended to disturb the gradient so that exact 

 differences could not be determined. The water as it left the 

 deaerating machine contained about 1 cc. of oxygen per liter and 

 this probably gave a minimum gradient of 5 cc. per liter at the 

 bottom of the experimental tank. The reactions of the fishes 



TABLE 9 



Showing the reactions of fishes to an oxygen gradient in boiled water. Numbers and 

 abbreviations as in table 6, p. 230. Experiment 72x was run with different fishes 

 from Experiment 72 because the fishes in 72 ivere not accustomed to seeing the experi- 

 menters and the results were interfered with by fright. Abbreviations as in Table 6. 



EXPT. 

 NO. 



02 

 IN CC. 



PER 

 LITER 



L H 



CROSS- 

 ED CEN- 

 TER 



TOTAL 

 TIME 



IN MIN. 



PER CENT OF 



TIME IN HALVES 



OF TANK 



Expt. 



H L 



Control 



H L 



TURNED BACK 



IN GRADIENT 



FROM HIGH (H) 



AND LOW (1?) 



Expt. 



H 



Control 



H L 



TEMP. 

 DEG. C. 



75 



72 X 

 72 

 73 



73 A 

 74 



74 A 

 76 

 69 

 69 A 



Lepomis 



Notropls 



Notropls 



Hybopsls 



Hybopsis 



Catostomua. 

 Catostomus. 



Abramls 



Ambloplltes. 

 Ambloplltes. 



11.7 



7.9 



7 



7 



7 



7.9 



7. 



11.7 

 12.0 

 12.0 



22 20 



33 



■9 



49 



125 



163 



3 



34 



15 



19 



(Exp. 9 

 [Con. 7 



8 



8 



9 



Average 2.7 9.552.6 47 20 56 44 46 54 4.5 12 



' One fish lay in the low oxygen over four minutes; cause unknown; control 

 often resting. 



^ No evidence of a reaction. 



' Fishes swam at the surface of the low oxygen end for seven minutes and thus 

 were giving a reaction to the vertical, but not to the horizontal gradient. 



