ADJUSTMENT OF FLATFISHES 457 



Thus it is plain that the shade assumed by the fish under the 

 influence of visual stimuli tends to be retained for a considerable 

 period after the latter are withdrawn. '^- 



Experiments with blinded fishes 



Any method of permanently destroying the sight of an animal 

 must necessarily involve a considerable nervous shock, and it 

 might be fairly objected, in the lack of further evidence on this 

 point, that such results as are described below may be due, in 

 part at least, to this shock, rather than to the loss of sight alone. 

 Thus any mere failure to respond adaptively after the operation 

 is not, in itself, a decisive proof that vision is a necessary element 

 in the reaction. Such doubts are, to be sure, greatly weakened in 

 the present instance by the fact that the blinding of one eye was 

 found to have little or no effect upon most specimens. 



In order to meet fully this objection that we may have to reckon 

 here with a ' shock' effect, I endeavored in the first place to use a 

 bandage of black cloth, fastened over the eyes. It was necessary, 

 however, to stitch this bandage to the margin of the head, and 

 this, of course, involved an injury to the fish. Moreover, the fric- 

 tion or pressure of the cloth soon damaged the eyes and led to 

 blindness. 



Accordingly, I gave up all attempt to blind the animals without 

 inflicting injury, "^^ and adopted the plan of cauterizing the surface 

 of the eyes with silver nitrate. This resulted at once in an opacity 

 of the cornea. After the lapse of a few days, the latter fell from the 

 eye, exposing its interior to the surrounding water. Even in this 

 condition, the retina (or optic nerve) frequently remained for some 

 days (7 or 8, in certain cases) decidedly sensitive to light, as was 

 shown by reflecting daylight upon the head with a mirror, or by the 



*2 For the pike, Mayerhofer (op. cit.) regards darkness as a "strong stimulus 

 to an extreme contraction of the chromatophores," since fishes which were thus kept 

 became much paler after a few days. On the other hand, Secerov and some others 

 report the acquirement of a deeper shade in total darkness. 



^^ The use of a coating of opaque material had been found to be impracticable 

 with Rhomboidichthys. 



