56 Herbert Eugene tValter 



To avoid the inconveniences of this method an attachment v^as 

 devised for directly dupHcating the path of a worm by means of 

 a style traveling over a sheet of smoked paper. The records thus 

 traced were made permanent by immersing the smoked sheets in 

 a weak solution of resin in alcohol and allowing them to dry, after 

 which the paths could be accurately measured and the rates com- 

 puted. 



The arrangement of this attachment, as seen from above, is 

 shown in Fig. 2. The diaphragm (Fig. i, H) has been removed 

 for the sake of clearness. At the tip of arm AF a style directed 

 upward comes in contact with the under surface of the aquarium 

 bottom (Fig. I, F)y while at the tip of arm B a similar style that 

 is pointed downward traces a line on the sheet of smoked paper L at 

 the left. After a little practice it was not difficult to keep the style 

 of arm A directly under the posterior end of a gliding worm, thus 

 duplicating its movements with considerable accuracy. The 

 expiration of any time interval can be indicated on the smoked 

 paper record by a crosswise scratch in the path. 



Arm A was rendered as non-reflecting as possible by black cam- 

 era paint as well as by being made triangular in cross section with 

 the apex of the triangle upward. Thus whatever rays struck it 

 from above were mostly either absorbed or reflected in a horizon- 

 tal direction, so that thevdid not reach the w^orm under experiment. 



b Results 



Rate of Locomotion. Planaria gonocephala moves somewhat 

 more quickly in non-directive light than it does in dark. Ten 

 apparently normal and representative worms were selected and 

 isolated in individual aquaria. They were kept in the dim light 

 of the dark room in water of the same temperature as that of the 

 experimental aquarium in which they were observed. At the end 

 of thirty-four days of experimentation these worms showed prac- 

 tically the same average rates under the same intensities of light 

 as they did at first. By alternating the individuals these trials 

 were so made that fatigue effects had little part in the results, 

 while the succession of light intensities was varied in such a way 



