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BLIND VERTEBRATES AND THEIR EYES. 



Experiment III: On May 13 the same 6 specimens were used under the same 

 conditions as in experiment I. The aquarium had been quiet since 5 p. m. the 

 evening before. 



» Two exchanged. 



• One other came out, went back. 



3 Two exchanged, the one last out returning. 



4 One came out, but went back at once. 



Experiment IV : On May 13, from 2 to 3 p. m., during the period correspond- 

 ing to the time when records were made the day before, the fishes stayed in the dark 

 chamber except occasionally when one would come into the light only to quickly 

 turn and swim back into the dark. 



Experiment V : On May 15 the fishes remained in their dark chamber nearly 

 all day except during the excitement caused by changing the water, when they 

 swam freely into the light. It is evident that the incessant changing during the 

 first observations recorded was due to excitement caused by the change of water 

 and aquarium. 



A small opening was made in the front of the dark chamber, through which 

 observations were made. A few individuals on this occasion came out. 



Experiment VI : On May 17 no blind fishes were in the light chamber between 

 8.30 a. m. and 9.20 a. m. Through an opening in the top of the dark chamber several 

 were observed to come to the opening between the two chambers but quickly to 

 withdraw. The sides of the light chamber were painted with a wedge-shaped dark 

 area the better to protect the dark chamber from oblique rays. 



Effect of jarring. — The aquarium was moved slightly in order to note the 

 effect of jarring. While no fishes had been in the light chamber during the morn- 

 ing, 4 were now out in a few moments; these returned and during 7 to 10 minutes 

 the changing to and from the dark chamber was kept up. 



At g*" 30'" 17 approach opening of dark chamber without going out. i6 approach corner above the opening. 

 .M g'' .?;'" drew off 2.5 inches of water to 0.5 inch from level of top of opening. 



At gi' 45'" one came to opening and returned; 7 went through opening. Evidently still some disturbance. 

 Left the observations at 9'' 48'". 



After the fishes had become quiet it was seen that while they were constantly 

 moving past the opening it was rare that one passed out into the light chamber, 

 and then they invariably showed signs of uneasiness, frequently turning sharply 

 round and reentering the dark chamber, at other times making a complete circuit; 

 this at a time when there was no direct sunlight. 



At 12 m. a dark tunnel was constructed by leaning a black pane of glass against 

 the dark partition, leaving an opening at the side of the aquarium opposite to that 

 in the opening of the first partition. For some time after this was done the fishes 

 stayed in the light chamber in which they had been put, without being able appar- 



