Il6 BIOLOGICAL LECTURES. 



certain fish without any definite regard for color. During 

 January, for instance, fish 3 moved out of the pink and orange 

 compartments but once ; fish I remained almost exclusively in 

 yellow, visiting pink once, orange once, and green four times. 

 Fish 2, on the other hand, remained mostly in violet, visiting 

 blue seven times and green three times. From this we must 

 conclude either that different individuals react differently, or 

 that one color does not produce a stronger reaction than an- 

 other, and the latter seems the more reasonable conclusion. 



To determine whether the apparatus had anything to do with 

 the distribution, and also whether widely separated elements of 

 the spectrum would cause the fish to react positively or nega- 

 tively, they were put into a rectangular aquarium impervious to 

 light, except at the ends, and divided by a median partition. 

 The ends were covered with translucent celluloid film, care 

 being taken, of course, to have each end equally light. 



In these experiments there was again conflicting evidence. 

 In general, it may be said that there was no marked difference 

 in the reaction to one or another of the rays of the spectrum. 



A similar series of experiments was conducted with Cholo- 

 gaster with the same reaction to white light, but with a marked 

 positive attraction by the red rays of the spectrum as against 

 the blue. 



A very positive series of observations has been made since 

 this was written. An aquarium two feet deep, four feet wide, 

 and about eight feet long was divided by a median partition to 

 near the bottom. Two lids were hinged at the top of this par- 

 tition. One or the other or both sides of the aquarium could 

 be covered at pleasure. Invariably, within a reasonable time 

 after one of the compartments was uncovered, all the fish 

 migrated to the dark compartment. 



Even more striking than this is the action of a colony of 

 Amblyopsis in an open pool. During the bright part of the 

 day, the fishes always remained under the rocks at the bottom. 

 In the morning and evening and at night, they could be seen 

 swimming about in various parts of the pool. 



