288 W. C. ALLEE 



The water is introduced through a circular tube 3 cm. in diameter, 

 which has holes to permit the exit of the water only on the side 

 away from the trough. The trough is 3 cm. across, 2 cm. deep, 

 and 50 cm. long. At its lower end it opens into another well 

 exactly like the one at the upper end. This in turn opens into a 

 drain way directly below the end of the main trough, the drain 

 being 1 cm. above the general floor of the apparatus. The whole 

 trough is made of wood and is painted a dead black with water- 

 proof paint. Thanks to the careful workmanship of Mr. Floyd of 

 the Ryerson Physical Laboratory, the trough is very accurate in 

 its dimensions. The animals were confined by wire gauze and 

 their movements measured by means of a centimeter scale at the 

 top of one side of the trough. When in use the apparatus was 

 kept almost level. 



The animals to be experimented upon, were placed in the cur- 

 rent at the center of the trough. They usually started off in 

 the direction in which they were first headed regardless of the 

 response which they would ultimately make. In some cases posi- 

 tive animals would continue with the current to the lower end and 

 then turn and make their way back along the edge of the trough, 

 toward the upper end. Usually they did not collect in contact 

 with the upper screen as Banta found to be the case in his experi- 

 ments. Rather the response brought a majority to the upper 

 part of the trough where they settled in the angles between the 

 bottom and the sides, with some of course clinging to the screen. 

 In taking readings the exact position of each individual was 

 recorded and an average taken of the position of the whole group. 

 From five to eight was found to be the most convenient number 

 to be tested at one time. A summary of the results obtained in 

 this manner, with normal stream Aselli, is found in table 5. 



Often the isopods would move first up stream and then down 

 stream, without giving a definite reversal. In these cases the 

 reversal time was taken to be the time after which there was no 

 decided movement against the current. When the experiments 

 ran over night no readings were taken after midnight. Except 

 ill the third and last experiments recorded in the table there was 



