allee] simple experiments IN ANIMAL BEHAVIOR 183 



After fifteen minutes start a current by stirring slowly with the 

 wrapped tweezers used in handling the animals. In order to 

 secure an even current run the tweezers five times around the pan, 

 near the edge and at a uniform rate. Gently stir all the animals 

 loose from the bottom. Take time for one minute after the 

 stirring stops and record the reaction of each animal. If an animal 

 goes against the current for forty seconds and with it for the 

 remainder of the minute it would be counted positive, while if it 

 goes with the current half the time and against it for the other half 

 it should be classed as indefinite. Trials should be continued in 

 this fashion until ten consecutive tests have been made. From 

 the results recorded the percentage of animals going positive, 

 negative, and indefinite to the current may be calculated, and the 

 animals rated accordingly. 



Results and discussions. — The results with isopods will depend 

 upon the habitat from which they were taken and on the time of 

 year. Pond isopods will give a low positive response while those 

 from streams will give a much higher percentage of positive 

 reactions, except during the breeding season when this may be 

 lowered. Amphipods show the same characteristics. Both the 

 fairy shrimp and the common shrimp will usually go against the 

 current. 



Minnows from one to three inches long are the best material 

 with which to demonstrate positive rheotaxis for class room 

 ptirposes. Almost any of the common minnows will swim vigor- 

 ously against the current reversing directly as the ciurent is 

 reversed. 



Geotaxis. 



Purpose. — To test for gravity acting as a stimulus. 



Materials. — Two glass cylinders, the larger the better; 500 cc. 

 graduated cylinders will do ; string or wire gauze ; sand and black 

 paper. 



Procedure. — Place a half inch of sand on the bottom of each 

 cylinder and fill with water. Arrange several strings so that they 

 hang from top to bottom, or roll a wire gauze cylinder and place 

 this with one end resting in the sand. Cover each cylinder with 

 black paper. Introduce into each from five to ten of the animals 

 to be tested and allow to stand fifteen minutes. Record the 

 position of the animals in inches from the bottom. Repeat the 

 observation at least five times. 



