MOVEMENTS, ETC., OF EKESII-WATRR PLANARIANS. 655 



-^^ per cent. — Weak positive reactions in nearly every 

 case. No negative reactions. The typical, complete food 

 reflex I have not been able to induce with sodium chh^ride. 



Concentrations below this do not produce any definite re- 

 action. 



In general, NaCl is a very ineffective stimulus to pla- 

 narians, either to the positive or the negative reaction. Dis- 

 tilled water is a considerably stronger stimulus to the positive 

 reaction. 



Sodium Bromide, 2 per cent. — Weak but distinct 

 negative reaction in all cases. 



I" per cent. — Well-marked positive reaction in nil cases. 

 Complete normal food reaction is produced. 



Potassium Chloride, 2 per cent. — The animals usually 

 react in a pecnliar way to this and stronger solutions of KCl. 

 When stimulated they stop, turn the anterior end either 

 slightly towards or slightly awny from the source of stimula- 

 tion, and then stay in the same place and squirm and twist 

 the body. In some cases there is a well-marked negative 

 reaction. 



i per cent. — Some specimens give negative reactions 

 in the fii'st few trials ; afterwards give definite positive 

 responses, ns do other specimens in all cases. In one case 

 the specimen gave marked positive reaction, and after the 

 head was turned towai'ds the stimulus, remained quiet in the 

 same position as long as the chemical acted. 



y*y per cent. — All specimens give positive reaction or 

 are indifferent. The whole food reaction took place on the 

 end of the tube. In this experiment it could be clearly 

 demonstrated that the })harynx is positively chemotactic to 

 this substance. It is probably positively chemotactic to all 

 substances which induce the preceding portions of the feed- 

 ing reaction. If, after the pharynx had been extruded, the 

 tube was turned about so that the ventral surface of the 

 animal could be seen, and the posterior part of the body was 

 moved with a needle, so as to change the position of the 

 pharynx with reference to the mouth of the tube, it could be 



