230 



EDWIN G. BOHI.V; 



In the course of experiments upon the modification of be- 

 havior in the flat-worm, the writer believes that he has observed 

 behavior that argues directly in favor of a differential sensi- 

 tivity; and it is the purpose of this note to describe the obser- 

 vations. 



MATERIAL 



The subjects used were specimens obtained from a stream 

 near Ithaca, New York, and were partially identified as Planaria 

 torva, although the identification was not absolutely positive. 



Keyboard for Lights 



APPARATUS 



The apparatus was set up in a dark room. The essential 

 features consisted of a circular glass tank, for which a crys- 

 tallization dish was used, 12.5 cm. in diameter by 6 cm. high, 

 and six 16 cp. electric lights (A, B, C, D, E, and F in the figure), 

 arranged in a circle about the tank, 15 cm. from its center, and 

 set at such a height that the centers of the bulbs were about 

 1 cm. above the level of the bottom of the tank. The lights 

 were so arranged that they could be individually thrown in or 

 out of circuit. They were controlled from a keyboard, which 

 was constructed of strips of tin. The strips were insulated at 

 the points of contact with the fingers, and so placed above a 

 metal rod, that each strip, when pressed down, completed the 

 circuit for a single lamp. One meter above the center of the 

 tank was suspended a single 16 cp. light. This light and the 

 system of lights below were controlled by a double-throw switch, 

 in such a way that when the lower lights were in use the upper 

 could not be, and vice versa. The tank was placed upon a sheet 

 of paper, ruled with four concentric circles of diameters, 12.5, 



