allee] simple experiments IN ANIMAL BEHAVIOR 181 



from the plates is shaded. This means that the animals under 

 experimentation must disregard either their optimum light or 

 their optimum touch relations. Usually they will disregard the 

 latter and come to rest in the darkened area thus showing that the 

 phototactic (response) is stronger than the thigmotactic response 

 of these animals. 



Thermotaxis. 



I. Purpose. — To demonstrate reaction to a temperature 

 gradient.'' 



Materials. — Four bread pans; two thermometers; a sink 

 with hot and cold water supply. 



Procedure. — Place two bread pans on the sink bottom parallel 

 with each other. Allow hot water to flow through one and cold 

 water through the other. Place a third bread pan that contains 

 one-fourth inch of water across the first two so that one end rests 

 in the cold, the other in the hot water. About two inches at each 

 end of the third pan should be exposed to each temperature. 

 Adjust the pans and the flow of water until the hot end of the 

 third pan is about 35 degrees C. Now empty this pan and place 

 in it one-fourth inch of water which has the same temperature as 

 that in which the experimental animals are kept. Put a similar 

 amount of the same water in another pan. Place ten to fifteen 

 of the animals to be tested in each pan. Place one of the second 

 pair of pans across the two already in the sink. Arrange it 

 precisely as the third pan above was arranged. Now place the 

 fourth pan near as a control. It should have the same light 

 relations as the experimental pan but should have the same 

 temperature throughout. As soon as possible after placing the 

 experimental pan in position hold a thermometer at each end and 

 observe the animals continuously. As the temperature rises at 

 the hot end what do the animals do? Compare their position 

 and actions with those of the control animals. Repeat using 

 lower temperature. Repeat using higher temperature but try 

 only a few animals as some are apt to be killed. 



Results. — As the water in one end becomes warm the animals 

 will move away. Those that visit that end in their roaming over 

 the entire pan will stay only a short time and will move rapidly 



*A gradient of any condition is furnished when a series of small changes 

 intervene between two extremes; thus when one end of a pan is at 6 deg. C. 

 and the other at 35 deg. C. with all intermediate stages present, a temperature 

 gradient is estabHshed. 



