MOVEMENTS, ETC., OF FRESH-WATER PLANARIANS. 663 



towards the end D in the majority of cases. In some few 

 instances an individual would give a weak positive reaction 

 (i. e. turn slightly towards <c) at some point in its course, but 

 this was so small iu amount that it did not in most cases 

 turn the animal directly towards x. Further, the direction 

 of movement was frequently changed considerably, and turned 

 away from x after this weak positive response. In other 

 words, the animals moved about in the trough practically at 

 random, giving only slight reactions in a few cases while in 

 the area of diffusion. Many of the individuals, after reaching 

 end D of the trough, turned around and went back to the 

 other end again, just as they would have done provided no 

 chemical had been present. Other specimens would glide 

 across the trough on the paraffin of the end D. Only these 

 specimens showed any deflnite response to the chemical. 

 When they came within the length of their own bodies from 

 the opening x they gave a well-marked positive reaction and 

 went to X. Having arrived there, they explored and 

 " gripped " the edge of the hole with the head, and then 

 extruded the pharynx. The pharynx was usually stretched 

 up into the diffusion opening, and the worm proceeded to 

 feed for a time on NaoCOo. 



These experiments were repeated many times with a 

 variety of chemicals of various concentrations, and diffusing at 

 various rates. It was very certain in all cases that there was 

 no definite orientation along lines of diffusing ions. When 

 the organism by chance came near the diffusion opening x, it 

 would give a positive reaction if the solution was of the pi'oper 

 concentration, and then proceed to give the complete food 

 reaction over the hole, but there was no continued orientation. 



There Avas a similar absence of a negative orienting 

 response when strong solutions of acids were used. In this 

 case the animals stayed at end C of the ti'ough, but this was 

 because when, in the course of their random movements, they 

 struck the diffusing chemical Avhere it was of sufficient con- 

 centration, they gave the usual negative reaction, turning the 

 anterior ends about 30"^ away, and starting off on the courses 



