THE SENSORY RESPONSES OF CHITON 225 



Experiment 1. 



11:15 A.M. A chiton placed with long axis parallel to the slot admitting 

 hght, distant 13 cm. from it. 



11:19 a.m. Oriented toward the hght. 



11:20 A.M. Began moving forward. At first moved in a diagonal di- 

 rection, until the girdle touched the side wall of the 

 container; it then turned further and moved directly 

 toward the light. 



11:24 A.M. Stopped, half-way toward the slot. 



1 1 :30 A.M. Began moving again. 



11:34 A.M. Reached light end and began climbing end wall. 



11:39 A.M. All except posterior quarter attached to end wall of con- 

 tainer. Stopped. 



11:43 A.M. Began again and moved until all of body was on vertical 

 end wall. Turned until body axis was parallel to water 

 line, where, just submerged, it lay directly over the slot. 



Experiment 2 



11:45 A.M. Same chiton as in experiment 1, placed transversely to the 



hght, but with other side illuminated, and 26 cm. from 



the light slot. 

 11:48 A.M. Began turning away from the light. 

 11:50 A.M. Had rotated away from the hght,^ then back toward it,, 



through an angle of more than 270°. 

 11:54 A.M. End had come in contact with side of container. Animal 



now began to climb. No forward progress toward the 



hght. 



Experiments 3 arid 4 



In two further chitons tested in this way, orientation was. 

 in one case direct, beginning almost at once; in the 

 other it required 29 min. (involving a preliminary turn- 

 ing through 45° away from the light). Both animals- 

 made definite progress toward the hght. 



These tests indicated in a general way the presence of a definite, 

 though sluggish, positive phototropism, with reference to dif- 

 fuse light. 



With direct sunlight, reflected horizontally from a mirror, 

 three individuals oriented promptly and move directly tow^ard 

 the light, two oriented toward the light and then aw^ay from it, 

 four individuals immediately oriented more or less away from 

 the light, and two did not move at all. This result obviously 

 required further analysis; it might have been the outcome of a 

 general illumination of the whole aquarium or might have ref- 



* Note this apparent persistence of a turning tendency once established- 



