120 JOURNAL OF SCIENCE. 



yellow chromatophores in the skin of those sides. Three showed very 

 well developed bands of pigment quite similar to that of the upper side 

 over the area occupied by the muscles of the longitudinal fins. The 

 other 7 specimens possessed a less quantity of pigment on the lower it 

 is true, but chromatophores were present in one part or another where 

 they are not present in the specimens living in the ordinary way on sand. 



The question of course arises, how are these pigment cells developed, 

 by migration from the upper side 1 from wandering lymphatic cells 1 or 

 from unpigmented cells already present in the same position before? 

 These questions I cannot at present answer, but am now endeavouring 

 to find replies to them. I think the third suggestion the most probable. 

 The chromatopliorss in flat-fishes are situated in the derma between the 

 surface of the scales and the epidermis. 



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 

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

 scarcely think any one will maintain that the condition of the specimens 

 in my experiment can be supposed to be a case of accidental variation. 

 On the other hand it is always possible that abnormal pigmentation on 

 the lower sides of free-living specimens is due to peculiarities of 

 environment or 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" * published in 1878, 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 transfer 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 metamor- 

 phosis 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 to Pouchet's researches on 

 chromatophorest 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 

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

 read Pouchet's paper referred to below, and can find no mention what- 

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

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

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



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



+ G. Pouchet, Des Changements de Coloration sous l'lnfluence des Nerfs. Arch, 

 de Physiol, et d'Anat. 1876. 



