31 



Of course I am well aware that specimens of flounders and other 

 flat-fishes are occasionally taken from the sea in which both sides are 

 colored, or in which there are colored spots on the lower side. But I 

 scarcely think any one will maintain that the condition of the speci- 

 mens in my experiment can be supposed to be a case of accidental 

 variation. On the other hand it is always possible that abnormal pig- 

 mentation on the lower sides of free-living specimens is due to pecu- 

 liarities of environment or of habit. 



I have other experiments in progress which I hope will further 

 elucidate the relation of the pigmentation of the flat-fishes to the action 

 of light. For the present I will conclude with a brief summary of what 

 previous writers have said as to the causes of the absence of chromato- 

 phores from the lower side. Prof. Alexander Agassiz in his paper on 

 the »Development of the Flounders« 1 published in 187S, says that the 

 attempt which he made of placing the glass dish containing young flat- 

 fishes at a height over a table, and thus allowing the light to come 

 from below as well as from all other sides, failed in arresting the trans- 

 fer of the eye, and also produced no effect in retaining the pigment 

 spots of the blind side longer than in specimens struck by the light 

 only normally from above. Prof. Agassiz in the first place did not 

 use a mirror, and in the second place he evidently expected that the 

 effect if any would be to arrest the metamorphosis. The idea on which 

 I found my experiments is that the inherited tendency will cause the 

 metamorphosis to take place even when the conditions are reversed, 

 but that when the reversed conditions are kept up long enough a new 

 metamorphosis will be induced in the opposite direction to the first. 



Prof. Agassiz refers in the same paper toPouchet's researches 

 on chromatophores 2 saying that they point most plainly to the partial 

 atrophy of the great sympathetic nerve, effected during the passage of 

 the eye from the right to the left or vice versa, as the cause of the ab- 

 sence of chromatophores from the lower sides of flat-fishes. I have read 

 Pou chefs paper referred to below and can find no mention what- 

 ever of any suggested cause of the absence of color on the lower sides 

 of flat-fishes. Pouchet found that section of the great sympathetic 

 put an end to the changes of color under the influence of light, but he 

 distinctly says that it made no difference whether the left or the right 

 eye was extirpated in the turbot. In either case the changes of color 



1 Proceedings Amer. Acad. Arts and Sc. Vol. XIV. 



2 G. Pouchet, Des Changements de Coloration sous l'Influence des Nerfs. 

 Arch, de Physiol, et d'Anat. 1876. 



