IV 

 NEUROHUMORS 



The preceding extended examination of the melano- 

 phore system in Fundulus leads to the conclusion that 

 the pituitary secretions in this fish in all probability play 

 no real part in its color changes, which seem to be con- 

 trolled exclusively by two sets of autonomic nerves, one 

 concentrating and the other dispersing in function. It 

 might seem that this would be the end of our quest, but 

 there are other phases of the subject that lead us on to 

 rather novel and interesting fields of inquiry. These 

 have to do with the way in which the nerves control the 

 melanophores, a process which is approachable in the 

 blanching of caudal bands in fishes. 



Dark spots produced on the skins of fishes by cutting 

 integumentary nerves were long ago recognized as tem- 

 porary. Pouchet in 1876 noted that these darkened 

 regions subsequently became as pale as the rest of the 

 fish, and von Frisch (191 1) observed that the contrast 

 between the dark area and the pale general surface of 

 a minnow may vanish in from twelve to fourteen days. 

 Smith (1931^), who worked also on the minnow, con- 

 firmed these early observations. When the ophthalmic 

 branch of the trigeminal nerve on one side of a minnow's 

 head is cut, a dark area appears and covers the anterior 

 dorsal aspect of the half of the head concerned. This 

 area disappears in the course of several days when the 

 fish is kept on a white background, but it does not dis- 

 appear when the fish remains on a black background. 

 This led Smith to the conclusion that some non-nervous 

 agency was here involved. This phenomenon was in- 

 vestigated in Fundulus by Mills (1932^) who showed 



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