MOVEMENTS, ETC., OF FRESIT-WATEK PLANARTANS. 649 



jrroos tlirono'li whole food rcnction on tlio end of tube. 

 The remainder still give weak negative reactions. 



■cTU P^^" cent. — Reactions essentially the same as in ^r— ^ 

 per cent. 



At this point this series was discontinued. It shows that 

 any absolnte concentration for a chemical solution which will 

 cause all planarians to give the positive reaction cannot be 

 assigned. How a given individual will react to a given 

 concentration of chemical depends almost, if not quite as 

 much, on the individual as it does upon the solution. 



Sulphuric, j\j- per cent, and -^ per cent. — Caused imme- 

 diate and violent reaction. Decapitated worm reacts like 

 normal. This is evidently a very strong stimulus. 



jij per cent. — Caused strong negative reaction in majority 

 of cases. One specimen reacted as follows : — the capillary 

 tube being held some distance away from the head, it 

 first gave a well-marked positive reaction. On coming 

 into the stronger solution near the mouth of the tube it 

 began strong convulsive contractions (evidently on account 

 of too sti'ong stimulation). Ifc remained, however, at the 

 same spot, and after a few minutes extruded the pharynx 

 and swept it about over the bottom. The specimen re- 

 mained this way for some time. The tube was, of course, 

 removed immediately after the first positive reaction was 

 given. A decapitated specimen in one case gave a very 

 distinct positive reaction to this solution, the tube being 

 held some distance away from the specimen. 



■giy per cent. — Negative reaction. Decapitated specimen 

 gave positive reaction once. Tliis solution, applied to 

 the posterior end of the body, induces the crawling move- 

 ment. 



Too" P^'^' cent. — Negative reaction. Isolated pharynx con- 

 tracts into a ball when stimulated with this solution. 



■j^jj per cent. — Positive reaction in one case. Remainder 

 negative. Same result with pharynx as in ji^ per cent. 



■^^j; per cent., y'^t^tt pcr cent., and ttttto pci' cent. — With 

 these solutions the reactions were for the most part negative. 



