52 COLOR CHANGES IN ANIMALS 



blood from pale or from dark fishes (Fig. 37). They 

 were produced from oil extracts, sterilized or not ster- 

 ilized, of pale fins, and from cold ether extract and 

 Soxhlet ether extracts from the same. These various 

 tests lead to the conclusion that the induced pale areas 

 in Mustelus are due to the action of some substance that 

 can be extracted from the pale fins of this fish by olive 

 oil or ether. The exact source of this substance cannot 

 be stated, for it has been taken from the whole pale fin 

 only. That it is not in dark fins and not soluble in 

 water leads to the conclusion that it is in all probability 

 the concentrating neurohumor concerned with the nerv- 

 ous blanching of Mustelus, but proof of this view is far 

 from complete. The few known properties of the sub- 

 stance are its solubility in olive oil and in ether, its 

 insolubility in water, and its resistance to dry heat up 

 to no° C. It is probable that even in the oily Soxhlet 

 extracts it was present at most in extremely small 

 amounts (Parker, 1935^). 



The only other fish that has been examined for the 

 possible presence of oil-soluble neurohumors is the cat- 

 fish Ameiurus. In this fish dark and pale phases are 

 well marked (Fig. 38) but the dark phase is the only 

 one favorable for study. Ameiurus (Parker, 1934^/) has 

 a melanophore system almost a duplicate of that of 

 Fundulus except that in addition to concentrating and 

 dispersing fibers Ameiurus has an active pituitary neuro- 

 humor which supplements the function of its dispersing 

 nerves. Extracts of the skins and fins of dark catfishes 

 were prepared as in the case of pale dogfishes, and the 

 final extract was injected subcutaneously into light cat- 

 fishes. This operation was followed in a little less than 

 an hour by the formation of dark splotches on these 

 fishes (Fig. 39). Such splotches, which were caused by 

 the dispersion of pigment in the melanophores of the 



