MOVEMKNTS, ETC., OF FRESH-WATKIJ PLANAT^IANS. 651 



tlie negative reaction the specimens were nearly or quite 

 killed. 



-^■^ per cent. — Convulsive negative reaction in tlie great 

 majority of cases. In one case stimulation was followed 

 by sharp positive reaction, succeeded by extrusion of the 

 pharynx. 



-^jy per cent, and J^ per cent. — A few specimens on some 

 trials give positive reaction, and then go into convulsive 

 twisting movements as they get into stronger solution. 

 Remainder negative. 



T^TT P^^' cent, and ^i- per cent. — Positive and weak nega- 

 tive reactions about equally divided. 



UTir P^^' cent, and y^rg-Tv P^i' cent. — Positive reactions 

 becoming proportionately more numerous. Negative re- 

 actions are very weak when given in response to these 

 solutions. In the cases where there is a positive reaction 

 the full response is not given; the specimens go up to 

 the mouth of the tube, but do not grip it nor extrude the 

 pharynx. 



Y5Vn P^^' cent. — With this solution all but one specimen 

 give the positive reaction. Specimens will follow the end of 

 the pipette about the dish if it is moved slowly. This is done 

 by a series of positive reactions. Specimens will give the 

 complete food reaction on the end of the tube. 



Citric, 2 per cent. — Strong negative reactions. 



1 per cent. — Less marked negative reactions. Tendency 

 to positive in some cases. 



Y*^ per cent. — Positive reactions in nearly all cases. Re- 

 mainder indifferent. 



YX) per cent. — Indifferent. 



Citric acid in weak solutions seems to be a ver}^ ineffective 

 sort of stimulus, not causing pronounced reactions of any kind. 



Formic, i per cent, and yV V^^ cent. — Prompt and de- 

 cided negative reaction. Causes a resting worm to give 

 a weak negative reaction of the anterior end, but does not 

 start the whole animal into movement, provided the tube is 

 withdrawn after the first reaction is obtained. 



