THE SENSORY RESPONSES OF CHITON 207 



top). During downward creeping their orientation is rarely 

 such that the long axis is strictly vertical. 



The following specific experiments show that the orientation 

 of the movement of Chiton is generally in an upward direction. 



1. Five chitons were placed, with their long axes horizontal, on the 

 walls of a flat-sided aquarium jar. They were located at about mid- 

 way between the bottom and the water line. The jar was removed 

 to a situation where the illumination was even and diffuse. Three 

 individuals moved upward to the surface of the water, and nearly 

 emerged; one oriented upward through an angle of 45°; the other one 

 oriented downward through an angle of 60°. 



2. Six chitons, placed as in the preceding test, were kept in the dark- 

 room for 1.5 hours. At the end of this period four were found to have 

 become oriented vertically, moving upward until almost entirely out of 

 water, one was oriented upward at an angle of 45°, and one had moved 

 upward to the water surface, being oriented upward at an angle of 

 about 45° from the horizontal. Another similar test was made with 

 eight animals, six of which oriented upward at various angles and two 

 downward; in this experiment the animals were overcrowded and 

 became piled upon one another. 



3. A similar test with five chitons, kept overnight in the dark-room, 

 gave four animals orienting upward and moving nearly out of water; 

 the remaining one had moved downward, assuming an orientation 45° 

 away from the horizontal. 



Of these twenty-four individual responses, twenty were 

 clearly such as involved an upward orientation from the hori- 

 zontal position. Since the animals continued creeping until 

 almost entirely out of water, it is hardly probable that want of 

 oxygen determined the observed behavior. This conclusion is 

 confirmed by subsequent tests in which chitons were placed in 

 dishes where anaerobic putrefactive processes had begun or were 

 allowed subsequently to begin. Frequently they did not creep 

 out of such dishes. Moreover, Chiton orients upward in a 

 closed vessel completely filled with water or one in which oxygen- 

 ated water enters from beneath. The negative orientation is 

 evidenced by animals of all ages. It is most perfectly ex- 

 pressed when the chiton is completely submerged. The hori- 

 zontal position assumed at the water level is a special conse- 

 quence of stimuli associated with the water level. 



The tendency to upward creeping is clearly evident upon 



