PIGMENTS ON THE LO\VER SIDES OF FLAT FISHES. 59 



but not exclusively, over the peripheral, or interspinous regions. In 

 the area of the upper side, which was previously unpigmented, there 

 were numerous small pigment spots. It is true that the amount of 

 pigmentation thus produced was not great, but it was perfectly distinct 

 and evident, and the duration of the experiment was less than six 

 months. It will easily be seen that this is a most remarkable result — 

 the most remarkable of all that I have obtained in the course of these 

 researches. It is not often in biological investigation that the result 

 of an experiment so exactly corresponds to the prediction, and it 

 affords very strong evidence that the view I advocated of the meaning 

 of the occurrence of unpigmented areas on the upper sides of ilat- 

 fishes, approximates closely to the truth. It may be objected that 

 possibly the formation of pigment would have occurred equally if the 

 lower side had not been exposed to light, and it would be desirable to 

 keep other piebald specimens for a length of time under normal con- 

 ditions. But it can scarcely be maintained that the unpigmented area, 

 when the fish was free, had been shielded from light, and that pigment 

 would have been produced in the aquarium merely in consequence of 

 the exposure of the upper side alone. We have no facts to indicate 

 that the peculiar distribution of pigment in these specimens undergoes 

 changes in the lifetime of the individual, in a state of nature, or in 

 the aquarium, under ordinary conditions. We can only hold, at 

 present, that the pigmentation is constant for the individual, under the 

 usual conditions, although in the face of the result here recorded, it 

 will be advisable to test this assumption. I hope, at some future time, 

 to publish figures shewing the specimen before and after the experi- 

 ment; but in the mean time have thought it well to place the result 

 on record. 



