THE DOGFISH 



L5 



Fig. 8. Dorsal view of a 

 pectoral fin from a dark dogfish, 

 Mustelus, showing a light band 

 about an hour after the initiating 

 transverse cut had been made 

 in the fin. Parker and Porter, 

 Biol. Bull., 1934, 66, pi. 1, fig. 1. 



centimeter long is made 



through a pectoral fin of 



a dark dogfish at right 



angles to the fin-rays and 



about a centimeter and 



a half from the edge of 



the fin, there will be pro- 

 duced a light band which, 



starting from the cut, 



will extend over the dark 



part of the fin to its pale 



edge (Fig. 8). The band 



will begin to appear in 



from ten to fifteen min- 

 utes after the cut has 



been made. It will reach its maximum in about a day, 



after which it will gradually disappear in from two to 

 three days. Light bands of this 

 kind can be excited even in dog- 

 fishes in the pale phase, show- 

 ing that the concentration of the 

 melanophore pigment in such a 

 band is more extreme than it is 

 in normal pallor (Fig. 9). The 

 pale bands produced by cutting 

 are not the result of circulatory 

 disturbances, for, as can be seen 

 under the microscope, their areas 

 even directly after the operation 

 show an active and apparently 

 normal circulation of blood. 

 Moreover in many parts of the 

 dogfish the nerves take very 



different directions from the blood-vessels and when 



cuts are made in these regions the blanched bands 



Fig. 9. Dorsal view 

 of a pectoral fin from a 

 pale dogfish, Mustelus, 

 showing a light band 

 several days after the 

 initiating transverse cut 

 had been made. Parker 

 and Porter, Biol. Bull., 

 1934, 66, pi. 1, fig. 4. 



