THE DOGFISH 17 



That the pale bands in Mustelus are the result of 

 nerve stimulation is rendered highly probable from the 

 following experiment (Parker, 1935^). If two needle 

 holes are made in the base of the anterior dorsal fin of 

 Mustelus, one about five millimeters in advance of the 

 other, and the two platinum electrodes of an induction 

 apparatus are inserted one in each hole, the preparation 

 after having been allowed to stand for half an hour or 

 so will show no change. If now the electric current is 

 started, in the course of ten minutes a pale band will 

 begin to appear in the fin and extend from a little above 

 the holes to the edge of the fin (Fig. 12). In twenty- 



Fig. 12. Anterior dorsal fin of a dark smooth dogfish, Mus- 

 telus, which has been stimulated to the formation of light bands by 

 a transverse cut near the anterior edge of the fin and by electric 

 stimulation posterior to this cut. The resultant light areas are 

 seen in the fin peripheral to the two regions of stimulation. 

 Parker, Biol. Bull., 1935, 68, 2, fig. 1. 



five minutes this band may become as distinct as that 

 produced by a cut. If in a given fin electric stimulation 

 and stimulation by a cut are started at approximately 

 the same time and in adjacent positions, two pale bands 

 will form, one from each center of excitation, and in a 



