76 



Herbert Eugene Walter 



just described was used. After the worm to be tested had been 

 placed in the inner aquarium and had begun gliding, it was so 

 oriented that the tip of its posterior end came precisely over the 

 center of the subjacent circle 10 cm. in diameter. The exact 

 time of its departure from the center of the circle was then noted 

 and the instant thereafter that the tip of the posterior end passed 

 over the circumference of the circle was again taken and the 

 worm's course plotted at once on a duplicate circle sheet. Each 

 worm was given four trials in this manner, being started in four 

 different directions, toward the light, away from the light, and 

 with the long axis of the body at right angles to the light, first 

 with one side to the light and then with the other. 



table xrn 



Amount of average deviation in 2400 trials expressed in degrees of a circle, exkibitedby negative planarians, 

 {Dendroccelum, Planaria and Phagocata), and a positive one (Bdelloura) when pointed toward, 

 away from, and at right angles to the source of light 



Direction in which the worm was pointed with regard 



At right angles 



Toward 



Away from 







48.1 

 49- 



128.7 27.3 

 39-3 112. 1 











The time of the worm's emergence from the circle was not taken 

 with a stop-watch because the observer's hands were otherwise 

 occupied. Instead a small clock, ticking half-seconds, was placed 

 conveniently near. By counting the number of ticks during the 

 interval of the worm's transit from the center to the circumference 

 of the circle the time consumed could be determined within less 

 than a half-second. After tracing the worm's course on a dupli- 

 cate circle sheet and measuring the same by means of a map 

 measurer, a unit of distance was obtained, which together with 

 the known unit of time consumed in covering this distance, fur- 

 nished all the data necessary for computing the rate of locomotion. 



Ten representatives of Dendroccelum lacteum, Planaria macu- 

 lata, Phagocata gracilis and Planaria gonocephala respectively 

 were given four trials apiece by the method just explained. The 

 results are presented in Table XIV. From the 160 records thus 

 obtained it becomes evident that the average rate of locomotion 



