THE STEREOTROPISM OF THE DOGFISH (MUSTELUS CALI- 



FORNICUS) AND ITS REVERSAL THROUGH CHANGE 



OF INTENSITY OF THE STIMULUS.* 



By S. S. maxwell. 

 {From the Rudolph Spreckeh Physiological Laboratory of the University of Cali- 

 fornia, and the Scripps Institution for Biological Research?) 



(Received for publication, July 18, 192L) 



In the preceding paper^ I have described certain contact reactions 

 of an elasmobranch fish, Rhinohatus productus, and I have shown that 

 these reactions are definitely tropistic in their nature. I pointed out 

 that in RhinohaUisthe response to a particular stimulus depends upon 

 two factors {a) the strength and {b) the location of the stimulus; 

 that, for example, a weak stimulus applied to the right upper surface 

 of the head causes the fins to assume an asymmetrical position of 

 such character that the body momentarily swerves to the left, and 

 at the same time the right side of the head is depressed; but a strong 

 stimulus applied at the same point brings about such a change in 

 the position of the fins as would arrest the forward movement of 

 the animal and cause it to dive to the bottom. The effect of both 

 these modes of reaction is to terminate the contact with the stimu- 

 lating object and hence they are both to be regarded as examples 

 of negative stereotropism. 



When I attempted to find out whether analogous reactions could 

 be obtained from other elasmobranchs I was at first greatly puzzled 

 by the behavior of the common dogfish. A dogfish tied down on the 

 shark board and supplied with a current of aerated sea water would 

 respond to stroking or scratching stimuli applied to the head or 

 snout with decided movements or changes or position of the fins; 

 but the results were often confusing or contradictory. A contact 



*The expense of this research has been met in part by an appropriation from 

 the Board of Research of the University of California. 



1 Maxwell, S. S., Stereotropic reactions of the shovel-nosed ray {Rhinohatus 

 producttis), J. Gen. Physiol., 1921-22, iv, 11. 



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