176 LESLIE B. AREY 



similar way. The effect of carbon dioxide is especially interesting 

 for, as it is the commonest catabolic product, it may have been 

 the agent that prevented movements in those cases. This con- 

 ception is opposed to Dittler's ('07) view, which assumes the 

 existence of a balance in the metabolism of the unstimulated 

 cone cells which is disturbed by the increased catabolism through 

 the action of light. The movement of the cone cells in the 

 isolated retina of the frog was stated by Dittler to be due to 

 the action of a weak free acid, the product of increased catabolism. 

 This conclusion, v/hich was supported by experimental evidence, 

 is opposed to that postulated by me; nevertheless, it must be 

 pointed out that the responses of the retinal elements differ 

 considerably in fishes and in the frog, and while evidence for 

 autoanaesthetization is indirect yet the results obtained from 

 experhnentation upon fishes can be consistently interpreted 

 in this way, whereas Dittler's hypothesis does not meet all the 

 known facts. A discussion of these points was given in another 

 section of this paper. 



E. EFFECT OF OXYGEN 



Spaeth ('13) showed that the isolated melanophores of Fundu- 

 lus contract in the absence of oxygen, but contracted melano- 

 phores do not expand when oxygen is the only stimulating 

 agent present. Fick ('90) deprived dark-adapted frogs of 

 oxygen by submergence in water or by introducing them into 

 an atmosphere of hydrogen or carbon dioxide. As a result of 

 this treatment he asserts that the retinal pigment underwent 

 expansion. Dittler ('07) states that. in frogs which are about 

 to hibernate the cones are never as fully elongated as in active 

 animals; but after subjection to an atmosphere of pure oxygen 

 the cones can again be obtained in the maximal dark position. 

 It seems probable that in this case the effect of oxygen was 

 indirect, and the increased activity of the cone cells accompanied 

 pari passu the return of other body activities. 



In order to test whether or not the amount of oxygen avail- 

 able to a fish in any way controls the distribution of its retinal 



