II 



THE DOGFISH 



The first fish whose chromatophore system I wish to 

 consider is the common smooth dogfish of the New Eng- 

 land coast, Mustelus canis. This fish was shown first by 

 Lundstrom and Bard (1932) to have a decided though 



limited color chanj 



On a white background it grad- 

 ually and slowly becomes pearly 

 white, often with a pinkish tint 

 due to the color of the blood 

 showing through its translucent 

 skin. On a black background 

 it darkens more quickly to a 

 deep slate color (Fig. 5). As 

 a microscopic inspection of its 

 skin shows, the pale phase is 

 due to a concentration of its 

 melanophore pigment (Fig. 6) 

 and the dark one to a disper- 

 sion of this coloring matter 



(Fig. 7). 



The dark phase was very 

 fully studied by Lundstrom and 



Bard. They showed that after 

 the pituitary gland had been 

 extirpated this fish began to 

 blanch in about thirty minutes 

 and reached full pallor in some 

 twelve hours. This pallor was 

 maintained even when the fish 

 was kept on a black background where under ordinary 

 circumstances it would have turned dark. The part of 



12 



the removal of the hy- 

 pophysis from the fish on 

 the right. They now 

 show extreme differences 

 in tint. Lundstrom and 

 Bard, Biol. Bull., 1932, 

 62, pi. 1. 



