MOVEMENTS, ETC., OF FRESFI-WATEK PLANARIANS. 647 



the solution stinkes to contract very violently, and the whole 

 animal to start crawling- ahead rapidly. This concentration 

 is very injurious, and if its action is continued, quickly kills 

 the individual. It will be noted that its effects are the same 

 essentially as those of strong mechanical stimuli applied to 

 the same parts of the body. 



Yy- per cent, and J^j per cent. — Results the same as in 4- 

 per cent. The animal is not as quickl}^ and extensively 

 injured by these solutions as by the former. It is to be 

 noted that with these comparatively strong solutions the 

 reaction time after stimulation of the posterior end of the 

 body is so slow that this part of the body is permanently 

 injured or destroyed before the animal gets away. 



■j-^ per cent. — In some cases a well-marked positive re- 

 action was caused by stimulation of the head region with 

 this solution. The head would turn towards the mouth 

 of the pipette in the characteristic fashion of the food reaction, 

 or the reaction to weak mechanical stimuli. In other in- 

 dividuals the reaction given was weakly negative, while still 

 other specimens were indifferent. In cases where there was 

 an indifferent reaction there was a local contraction of the 

 side of the head stimulated. 



-gjj per cent. — Clearly marked positive reaction in large 

 majority of cases after the stimulus has acted for some 

 time. This solution never caused the negative reaction. Some 

 individuals were, in a few cases, indifferent to this solution. 

 This solution is too weak to start a resting specimen into 

 movement. 



liio V^^' cent, and weaker. — Indifferent reactions or weak 

 positive. 



This acid appears to be a very strong stimulus for the 

 negative reaction in concentrations down to y\, per cent., 

 while below that it is a rather ineffective stimulus, and the 

 reaction when induced is positive. 



Hydrochloric, yV P*-*^" <^<-'"t- — Strong negative reaction. 

 There is noticeable in some cases a tendency for some 

 individuals to turn very slightly towards the source of 



