1923] Atsatt: Behavior of the Leaf -nosed Snake 307 



EESPONSE TO STIMULI 



The snake's movements seemed little controlled by a positive 

 reaction to contact. To be sure, it traveled along the edge of the box 

 rather than across the open surface of the sand but occasionally it 

 did go across. When the thermometer was in the box it glided over 

 this object or between it and the nearby side of the box. The snake 

 crawled under a rock, under a piece of palm leaf and out again, but 

 it crawled over small strips of glass so fixed that they offered easy 

 opportunity to crawl under them. Light here seemed to play a more 

 important part than contact in determining the course of progress. 



One problem was to determine whether the activities of the snake 

 were controlled by response to light, or to heat, or both. The negative 

 response to direct sunlight was very marked. When the reptile was 

 first found, shortly before noon, it was in a depression under a rock 

 and hence in the dark. When it was transferred to a tin box with 

 holes punched in the top it hid itself in the sand. On April 4, on a 

 warm afternoon when the open box of sand was half in sunshine and 

 half in shadow, the snake always turned away when it found itself 

 in the direct sunshine. It would pull back its head sharply when 

 only half an inch of the head extended into the area of sunlight. 

 Occasionally it would get more into the light but it always went 

 back promptly into the shade. Finally it buried itself in the sand. 

 On the next day when no direct sunlight fell on the sand a flat 

 mirror was used to throw a beam of light on the snake's head. The 

 snake responded immediately by turning away to get out of the spot 

 of light. It did this repeatedly and finally buried itself to get rid 

 of the annoj^ance. On April 18 record was kept of the snake turning 

 back sharply from bright sunshine twenty-five times in as many 

 minutes. The response was as consistent at the end of that period 

 as at the beginning. Furthermore, when the snake was kept in a 

 can with only a few holes in it and placed in a cool dimly lighted 

 room, the animal was quiet on the surface of the sand. It was invari- 

 ably found on the surface when the cover was lifted either in the 

 daytime or at night. 



An experiment on combined temperature and light control was 

 undertaken on April 13 in a room with dim daylight. An electric 

 bulb with reflector was placed seven inches above the can containing 



