STEREOTROPIC REACTIONS OF THE SHOVEL-NOSED RAY, 

 RHINOBATUS PRODUCTUS. 



By S. S. maxwell. 



{Fram the Rudolph Spreckels Physiological Laboratory of the University of California, 

 and the Scripps Institution for Biological Research.) 



(Received for publication, June 14, 1921.) 

 I. 



It has been pointed out by Loeb^ that our orientation in space is 

 determined mainly by three groups of tropistic influences; namely, 

 light, gravitation, and contact. Light and gravitation cause the 

 orientation of organisms through effects upon muscle tonus. When 

 the lines of force strike the animal obliquely, as for example, when 

 light rays fall unequally on the two eyes, the unequal stimulation 

 causes differences of tonus on the two sides, and the symmetrically 

 placed muscle groups acting with unequal strength, bring about forced 

 changes in the direction of locomotion. When the lines of force 

 coincide with the axis of symmetry, or the plane of symmetry of the 

 body, the effects are equal on the two sides and movement can go 

 forward in a straight line. For the contact, or stereotropic, reactions, 

 quantitative relations of this nature have not heretofore been 

 described. 



In my studies on the physiology of the labyrinth I have found it 

 necessary to distinguish carefully between those eye and fin move- 

 ments which result from excitations of end-organs in the ear, and 

 movements which arise from other sources. In this way I have come 

 to make observations on the contact reactions of the shovel-nosed 

 ray, or guitar fish, Rhinohatus productus, which will, I believe, throw 

 important light on the nature of stereotropic reactions in general. 



Rhinohatus is not so broadly expanded as most of the other rays. 

 The pectoral fins, however, have the characteristic fleshy thickened 



' Loeb, J., Forced movements, tropisms, and animal conduct, Philadelphia 

 and London, 1918. 



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