44 . A. M. REESE 



REACTIONS TO GREEN LIGHT 



Experiment XIX. — The arrangement of this experiment dif- 

 fered from the last only in the substitution of a green filter for 

 the blue. This filter consisted of solutions of copper chloride 

 and potassium monochromate, after the formulae of Landholt, 

 in jars like those described in the two preceding experiments. 

 The same nine animals were used; they had been in total dark- 

 ness for twenty-nine days, and had been fed upon earthworms 

 the day before the experiment. In 30 observations, at five- 

 minute intervals, 210 animals faced the green light to 51 that 

 faced away from it; and 199 animals were found in the near 

 half of the aquarium to 71 in the half farther from the light. 



The attraction of the green light is apparently more marked 

 than the blue but less marked than the red. 



REACTIONS TO WHITE LIGHT ON VARIOUS PARTS OF THE BODY 



Experiment XX. — In order to be able to throw a small, sharply- 

 defined spot of white light on any part of an animal a small 

 electric bulb was mounted in the tube of a microscope, as de- 

 scribed by Bradley M. Patten in Science, January 22, 1915, 

 pp. 141-2. By using different low-power objectives a sharply 

 defined spot from 1 to 5 mm. in diameter was directed upon all 

 parts of the body of several animals. These animals were in a 

 black rubber developing tray in sufficient water to cover them. 

 In one case they had been in a dark room only an hour; in 

 another series of trials they had been in the dark for a week or 

 more. Some of the animals were of the lighter shade with very 

 bright crimson spots; other animals were of the darker type 

 when experimented upon. During experimentation just enough 

 light was admitted to the dark room to faintly see the animals, 

 so that any movement could be noted. The spot of light was 

 thrown, as has been said, on all parts of the body, from the head 

 to the tip of the tail ; on the crimson spots and between them ; it 

 was varied in diameter from 1 to 5 mm. No certain reactions 

 could be determined for any of the animals used. Doubtful 

 reactions were sometimes obtained when the spot was made 

 large enough to cover the entire anterior half of the head. 



When the spot was thrown on the black bottom of the tray 

 near the animals they followed it actively and snapped at it, 

 evidently taking it for food; they seemed to be able to see the 

 spot at a maximum distance of about 3 cm. 



