308 University of California Puilications in Zoology [Vol. 21 



the snake. In eight minutes the temperature of the air rose from 

 28° C to 34°. The animal made frantic attempts to bury itself in 

 the sand in the usual manner and it also attempted to dig. When 

 the light was snapped off the snake remained quiet on the surface of 

 the sand. After the temperature had dropped several degrees the 

 light was turned on again. The temperature rose half a degree in 

 the quarter of a minute that elapsed before the snake began to move. 

 Again the light was turned off and the animal immediately became 

 quiet. When the temperature had dropped lower than at the start 

 the light was turned on. The snake became active and continued 

 active until it seemed to be becoming exhausted. Again the light 

 was turned off. When next the light was turned on, the snake buried 

 itself in the sand. 



The following day an effort was made to test the effect of tem- 

 perature alone by using a dark room with red light and a box with 

 warmed sand at one end and cool sand at the other. The sand at the 

 warm end varied because of cooling from 47.8° C to 41° and at the 

 cool end from 27.5° to 25.3°. The snake moved around actively and 

 shoM-ed no differences in reaction on warm and cool sand. When 

 the red glass was withdrawn so that electric light came on the snake 

 from above and to the right the snake generally withdrew from the 

 light into the shadow cast by the right end of the box. It did not 

 always do so ; occasionally it crawled into the light. When it was 

 transferred to cooler sand, with the warm end 37.6° to 34.2° and the 

 cool end 27.5° to 26.4°, the snake showed no reaction to temperature. 

 As long as the white light was on, the animal spent more time in the 

 shadow than in the light. If it got its head into the light it withdrew 

 it. It made few attempts to get into the ground at either the warm 

 or the cool end but tried to get out over the low wall of the box. 



On April 18 in a box of sand partly in direct sunshine and partly 

 in shadow the snake consistently drew back from the sunshine. The 

 can was turned at intervals so that the warm sand was in the shadow 

 and the cool sand in the sun. The snake moved into the shade and 

 thereby into much warmer sand. 



On April 15 the effect of light was studied while the factor of 

 temperature was eliminated as far as proved possible. Over the box 

 of sand Avas placed a crystallizing dish containing a blue solution 

 (alkaline copper sulphate) three or four inches deep, to cut out the 

 red heat rays. The temperature of the sand in sunshine was 37° C; 

 under the blue light it was 33.5° at the start and 31° twentv minutes 



