or sOo ITius, in the contrxjl condition, listed in table 2, the 

 fish entered the field 3 times diiring the first 2 minutes, but 

 not thereafter. 



In Experiments 3 to 6^ colored filters were used. With the 

 red filter, the tuna entered the field 13? lU, and 17 times in 

 three separate experiments o With the green filter j, the tuna 

 entered tlie field 13 times in one experimento Under control 

 conditions, as before, there were only 3 entrances « Ihe pattern 

 of movement was similar to that with white light o 



Apparently both white and colored continuous light from 

 the horizontally projected arc-light beam caused a similar 

 tropistic movements Unfortunately, experiments with a blue fil^ 

 ter were interrupted by noise emanating from nearby buildingso 



Series ii— Reactions to rad ia ting light from bulbs 



The results of experiments with continuous and interrupted 

 radiating light from a plain 200-watt (2l5 foot candles) and a 

 painted 200-watt (106 foot candles) electric light bulb are 

 shovm in table 3» "H^e painted bulb, with a slight orange hue, 

 was used because it happened to have been equipped with a water- 

 proof socket, it had been used previously in night lighting for 

 fish larvae,, Tv\ro yellowfin and five tunny were present. 



Experiments 1 to 5 were performed with continuous light 

 from the two bulbs. In Experiments 1 and 2, which were made at 

 dusk (6sitO and 6s5'5 Ponio) there was no positive reaction, the 

 tuna entering the field fewer times during the experiment than 

 during control conditions, Ihe negative results may have been 

 due to the fact that it was not quite dark when the experiments 

 were made, A half-hour later, positive tropism was shown in 

 Experiments 3 and 1; with lit and 12 entrances into the field as 

 compared with h under control conditions <> At times the yellow- 

 fin entered the iield by themselves^ at other times they joined 

 the school of tunny, which entered as a unito In Experiment ^g 

 with the plain bulbj there were only 6 entrances, but this may 

 have been due to interference caused by the approach of on= 

 lookers to the south wall of the tank towards the end of the 

 5-minute test period. It is concluded that, after dark^ the 

 tuna show tropistic response to radiating light from bulbs with 

 intensities of 21^ and 10 6 foot candles. 



In Experiments 6 to 10, the plain and painted bulbs were 

 interrupted at a rate between 60 and 75 times per minute, with 

 the light and dark period of the same durations The number of 

 entrances with the painted bulb (11, llj and 7) was greater 

 than with the plain bulb (0 and U) . The latter did not differ 

 appreciably from control conditions. However, observations 



h5 



