THE KILLIFISH 39 



dominant concentrating innervation. But this point, 

 so far as I am aware, is purely speculative. 



Evidence for double innervation such as that which 

 has been presented is not easily and quickly gathered. 

 The only other fish that has been exhaustively studied 

 from this standpoint is the common freshwater catfish, 

 Ameiurus nebulosus, whose melanophore system (Par- 

 ker, 1934^) appears also to involve two sets of nerves. 



Perhaps the most important advance made in the 

 physiology of chromatophores during the last decade 

 and a half has been the establishment of the fact that 

 pituitary secretions are often of the utmost significance 

 in color changes. Now what part do these secretions 

 play in the melanophore activities of Fundulus} To 

 test this question Matthews (1933) removed the pi- 

 tuitary glands from a number of killifishes, and after 

 their recovery he subjected them to changes of environ- 

 ment to ascertain whether they had lost to any extent 

 their capacity to alter their tint. Having observed no 

 such loss Matthews concluded that this gland in Fun- 

 dulus was of little or no importance in controlling color 

 changes. Matthews, however, made the interesting ob- 

 servation that an extract from the pituitary gland of 

 this fish when applied to an isolated scale was followed 

 by a concentration of pigment in the melanophores of 

 the scale. Rather the reverse of this effect was recorded 

 by Kleinholz (1935) who showed that when pituitary 

 extract from a Fundulus was injected into another on 

 whose tail was a partly blanched caudal band, this band 

 darkened though the fish as a whole did not. These 

 various observations demonstrate that under normal 

 conditions the pituitary gland in Fundulus is probably 

 of no importance in the control of the color changes, 

 though the exceptional responses obtained from its se- 

 cretion as applied to isolated scales by Matthews and 

 to caudal bands by Kleinholz call for further elucidation. 



