242 VICTOR E. SHELFORD AND W. C. ALLEE 



experiments as we are about to describe. The stock used was 

 divided into two parts; one in tap water, and the other in water 

 with less than 1 cc. of oxygen per hter. 



1. High oxygen stock. Nearly all the fishes kept in tap water 

 reacted with some distinctness to the boiled water, but con- 

 sidering only time preferences, the Etheostoma and the Amblo- 

 plites did not react to the gradient, since they showed a time 

 preference for the boiled water in some experiments and for tap 

 water in others. All the others gave a preference for the tap 

 water, though in many cases it did not exceed that shown for 

 one end of the control where the two ends were identical. For 

 example, the control individuals of Hybopsis (experiment 10) 

 spent 90 per cent of the time in one end of the tank, the experi- 

 mental fishes only 76 per cent in the tap water of the experiment. 

 Such cases are explainable when we consider the amount of 

 activity as indicated by crossing the center in experiment and 

 control. The control fishes in this case crossed the center only 

 one-sixth as many times as the experimental fishes. This was 

 characteristic and was probably due to the stimulating effect of 

 encountering a change of water. 



The fishes which reacted with greatest precision to the boiled 

 water gradient were Hybopsis (chart 4, experiment 71), Microp- 

 terus, and Notropis (table 11). The reaction of Lepomis in experi- 

 ment 13 serves as a typical case of the reactions to the boiled 

 water. The fishes showed a time preference for the tap water 

 and ten turnings back from the boiled against six from the tap. 

 The turnings of Lepomis and Hybopsis, which react similarly, 

 were not characterized by any striking movements of the mouth 

 or opercles though in the experimental tank the fishes showed a 

 disturbance due probably to lack of oxygen. That is, they gave 

 characteristic risings to the surface and gulpings with emission 

 of air bubbles, in the boiled water end, and some hesitation in 

 crossing the center, not shown in the control. Micropterus is 

 apparently one of the most sensitive of fishes. Our original 

 stock consisted of only four specimens, three of which died in 

 water containing less than 1 cc. of oxygen, while confined there 

 in the second experiment attempted (see p. 245). In the one 



