22 



STEREOTROPISM OF THE DOGFISH 



tail turn toward the stimulated side. The effect of these as a steering 

 apparatus would be to change the course toward the stimulated side; 

 e.g., turning the dorsal fins or the tail to the left would cause the 

 course to swerve to the left. But in addition to this another effect 



TABLE I. 



Mustelus calif ornicus , 33 Inches Long, May 20, 1921. 



The first column indicates the strength of stimulus; the second, the side of the 

 liead to which it is applied; the third, fourth, and fifth, the direction of movement 

 of the first and second dorsal and the tail fins respectively. The last two columns 

 give the direction of movement of the anterior border of the right and left pectoral 

 fins; and, in these two columns, / at the end of the word indicates that the 

 posterior end of the fin was higher than the anterior; \, that the posterior margin 

 was lower than the anterior. 



would result. When a dorsal fin turns to the left it assumes an oblique 

 position; that is, it is its posterior border which goes to the left most 

 strongly. Its resistance as the animal moves forward in the water 

 would have a screw effect, tending to rotate the body around its 

 longitudinal axis so that the ventral side would be turned in the di- 



