232 VICTOR E. SHELFORD AND W. C. ALLEE 



t eristic of Umbra and Notropis. For example, Umbra in experi- 

 ment 49 (table 6, p. 230) tried the high carbon dioxide during 

 the first three minutes, began rising to the surface after about 

 two-and-one-half minutes and turned back from the center dur- 

 ing the next three minutes, then tried the high concentration 

 during the two minutes following. After this the fishes remained 

 for eleven minutes in the low end, spending much of the time at 

 the surface and turning back often only a short distance away 

 from the low end. In chart 1, experiment 48 A, the bullheads 

 tried the highest concentration during the first two ininutes, went 

 only to the center during the next five minutes and then rested 

 in the low end for fourteen minutes. They then tried the higher 

 concentrations during the four minutes following and came to 

 rest in the low end remaining there until the end of the 

 experiment. 



The invasion of the high carbon dioxide was in nearly all 

 cases followed by several turnings back at the center or resting 

 in the low end. The sensitiveness of the fishes appeared to be 

 in some way affected by exposure to the high concentration and 

 the invasion of the high concentration was not repeated for' some 

 time. This is true in a general way of all the fishes and for all 

 the concentrations. This tendency appears in the reactions of 

 Abramis to the low concentrations (experiment 85, chart 1). 

 An inspection of the graph here shows that in the second half of 

 the experiment considerable time was spent in the high end, 



Chart 1 Showing the reactions of fishes to a carbon dioxide gradient in tap and 

 in boiled water. For concentrations, see tables 6 and 7. The space from right to 

 left between the scales represents the length of the tanks in which the fishes went 

 back and forth. The broken vertical line represents the centers of the tanks; 

 the character of the water flowing into the ends of the tanks is indicated at the top 

 to the right and left sides of the space. The vertical distance represents numbered 

 minutes, which are subdivided into ten second periods. The lines as drawn, where 

 horizontal, represent the movements of the fishes; and vertical, the resting of the 

 fishes. The method of representing the facts is shown in the experimental portion 

 of experiment 55. The fishes rested most of the time in the tap water end but 

 made occasional excursions to or beyond the center of the tank; the duration of 

 these is indicated by the scale at the left. The number of fishes used is indicated 

 in front of the scientific name of the species. The dotted lines represent the move- 

 ments of a single fish ; the solid lines of two or three fishes as the case may be. 



