526 ELECTRICAL SENSES 



orient with respect to uniform electric fields such as those induced by ocean 

 currents flowing through the earth's magnetic field (passive electro- 

 orientation). These fields typically measure from 0.05 to 0.5 /iV/cm (Von 

 Arx 1962). At the present writing, the stingrays have learned to orient 

 perfectly well in uniform d.c. fields as low as 0.04 //V/cm, which proves 

 their ability to detect the direction and polarity of the oceanic electric 

 fields. During these tests, the horizontal component of the earth's local 

 magnetic field is nulled, whereas the vertical component is left undisturbed. 

 By gradually lowering the electrical field strength, we will establish the 

 threshold of response. Yet, the significance of many other natural and man- 

 made voltage gradients in the ocean remains to be evaluated. Obviously, we 

 still are at a pioneering stage and a long way from a full understanding of the 

 electric and magnetic sensory biology of sharks, skates, and rays. 



ACKNOWLEDGMENTS 



I thank Drs. Sven Dijkgraaf and Theodore H. Bullock for their active interest 

 in my research. Kenneth J. Rose, William L. Ackerman, and Vera Kalmijn 

 volunteered to participate in the field work and magnetic experiments. 

 Clifford A. Kolba and Richard T. Nowak have been most helpful in preparing 

 the manuscript. These studies were conducted under contract with the Office 

 of Naval Research (N00014-74-C-0262). Funds for the observation platform 

 were generously provided by the Eppley Foundation for Research. This is 

 contribution no. 4109 from the Woods Hole Oceanographic Institution. 



REFERENCES 



Akoev, G. N., O. B. Ilyinsky, and P. M. Zadan. 1976. Responses of 

 electroreceptors (ampullae of Lorenzini) of skates, to electric and magnetic 

 fields. J. Comp. Physiol. 106:127-136. 



Andrianov, G. N., H. R. Brown, and O. B. Ilyinsky. 1974. Responses of 

 central neurons to electrical and magnetic stimuli of the ampullae of 

 Lorenzini in the Black Sea skate. J. Comp. Physiol. 93:287-299. 



Bennett, M. V. L., and W. T. Clusin. 1978. Physiology of the ampulla of 

 Lorenzini, the electroreceptor of elasmobranchs. Pages 483 to 505 in 

 Sensory biology of sharks, skates, and rays. Edited by E. S. Hodgson and 

 R. W. Mathewson. Office of Naval Research, Arlington, Va. 



Bigelow, H. B., and W. C. Schroeder. 1953. Fishes of the gulf of Maine. 

 Fish Bull. 53:1-577. 



Brown, H. R., and O. B. Ilyinsky. 1977. Electroreceptors and magnetic field. 

 Proc. Int. Union Physiol. Sci. 13:99. 



Dijkgraaf, S., and A. J. Kalmijn. 1962. Verhaltensversuche zur Funktion der 

 Lorenzinischen Ampullen. Naturwissenschaften 49:400. 



Dijkgraaf, S., and A. J. Kalmijn. 1963. Untersuchungen liber die Funktion der 

 Lorenzinischen Ampullen an Haifischen. Z. Vgl. Physiol. 47:438-456. 



