68 J. FRANK PEARCY AND THEODORE KOPPANYI. 



around any one of these axes the eyes move as if to retain their 

 original position in space, or to preserve the original visual field." 



We think that the tilting is due to so-called "voluntary" 

 motor attempts of the fish to regain or retain the usual visual 

 field. 



Heliotropic reactions involve different mechanism in fish than 

 in the invertebrates, for Parker has shown that the dogfish, when 

 only one optic nerve is cut, never moves in circles. 



Since in the tank, where the fish lived, there were diffused light 

 conditions, there was no single source of light that could act as a 

 phototropic stimulus. Interpretation of the tilting as a simple 

 phototropic response seems therefore excluded. 



The tilting at 45 was the optimal condition for the animals to 

 see the walls of the aquarium and most of the environment with 

 which he can come in contact and our results indicate that the 

 tilting is a quick reaction of the organism as a whole. 1 



SUMMARY. 



1. The dislocation of one eye into the top of the head and the 

 removal of the other eye produce a tilting of the whole body with 

 its dorsoventral axis 45 to the side of the vertical. The reposi- 

 tion of the dislocated eye into its original orbit changes the 

 orientation and equilibrium of the fish immediately, it regains its 

 normal position in swimming and at rest. 



2. The tilting is probably due to the attempts of the animal to 

 keep its usual visual field. 



The writers wish to express their thanks to Professor A. J. 

 Carlson for his constant help and encouragement. 



BIBLIOGRAPHY. 



1. Lyon, E. P. Amer. Jour. Physiol., III., 86, 1900. 



2. Parker, G. H. Bulletin of the Bureau of Fisheries, XXIX., 45, 1909. 



3. Lee, F. S. Amer. Jour. Physiol., I., 128, 1898. 



4. Steiner, T. Sitzungsberichte der K. preussischen Akademie d. Wiss., XXXII., 

 539. 1886. 



5. Loeb, J. Pfliiger's Archiv, XLIX., 175, 1891. 

 5a. Loeb, J. Pfliiger's Archiv, L., 66, 1891. 



6. Bethe, A. Pfliiger's Archiv, LXXVI., 470, 1899. 



7. Bigelow, H. B. American Naturalist, XXXVIII., 275, 1904. 



8. Maxwell, S. S. Labyrinth and Equilibrium. T. B. Lippincott Co., 1923. 



1 If so, then the fish placed in the dark or by cutting its only optic nerve should 

 regain its normal position. We contemplate to investigate this and related problems 

 in further experiments. 



