648 RAYMOND PKARL. 



stimulation before giving' tlie strong negative reaction. 

 Stimulation of the anterior end of a decapitated specimen 

 caused a slow negative reaction with long reaction time. 

 This solution causes the change from the glide to the crawl 

 when applied to the posterior end of a normal worm. 



yV per cent. — Negative reaction; rather weaker than with 

 preceding solution. With this solution one specimen would 

 turn towards the source of the stimulus until the head came 

 into the strong acid near the mouth of the pipette, and then 

 give the sharp negative reaction. 



:f J per cent. — Specimen A gave positive reaction in every 

 case ; specimen B in about 50 per cent, of all cases, while 

 iu the remainder of trials gave weak negative. Other 

 specimens negative reaction. 



^L per cent. — Specimen A as in preceding case. Specimen 

 B gave positive reaction in about 90 per cent, of all trials. 

 Other specimens weakly negative reactions. 



Y^jj per cent. — All specimens give well-marked positive 

 reaction. They glide up to the end of the capillary and 

 "grip" it with the anterior end as in the food reaction. 

 After holding on for a moment they let go and give a sharp 

 negative reaction, indicating that the stimulus is still too 

 strong when continued. This behaviour will indicate the 

 machine-like character of the positive reaction. 



■^Q per cent. — In the majority of cases indifferent re- 

 action. Remainder positive. 



To give an idea of the dependence of the reactions to 

 chemicals on the physiological condition of tlic organism, the 

 following series of experiments with HCl in solutions of y-^^^ 

 per cent, and weaker concentrations may be described. It is 

 to be understood that these experiments were carried out 

 on different animals from those just given. 



y-g^ij per cent. — No sharp positive reaction. Specimens 

 Avill give a weak negative reaction if the opening of the 

 capillary is held very near the head. In most cases reactions 

 are indifferent. 



^TU" P^^* cent. — One specimen gives positive reaction and 



