Reactions of Aiolosoma to Chemical Stimuli 69 



The fact that only experiments with electrolytes are recorded 

 here suggests an interesting problem from that point of view. 

 Several hundred tests were made with the non-electrolytes — urea, 

 cane sugar and glycerine, — but with negative results. An effort 

 is now being made to find a non-electrolyte that will stimulate a 

 characteristic reaction, similar to any of the above. After these 

 experiments are concluded, something further may be determined 

 as to the role of electrolytes in this field. The fact that Pearl 

 ('03) stimulated a similar turning of the anterior part of the flat- 

 worm — equivalent to our exploring movement — by means of a 

 light touch with a piece of wood, suggests that the secret of this 

 reaction lies within the confines of the animal economy. We 

 therefore, conclude, for the present, that the turning toward the 

 stimulus in the case of ^Eolosoma, is due to a sense of chemical 

 change; to a difference in intensity arising locally in the animal's 

 environment. The movement was not an orientation. 



Associated with this turning of the head the exploring move- 

 ments were expressed. The animal then moved toward the source 

 of the chemiical, exhibiting the feeding reaction, or away from the 

 same by means of a slow crawling movement. The positive reac- 

 tions were due to the fact that the weak solutions of the carbonates 

 or iron sulphate stimulated certain internal changes akin to those 

 induced by food particles. It is interesting to note that with a 

 rise in the temperature of 5° C, or more, the animal uniformly 

 responds negatively to these stimuli. The ability of these solu- 

 tions to stimulate the feeding reaction is thus conditioned by the 

 physiological state of the organism — by its previous internal reac- 

 tions to external changes in its environment. 



As the concentration of the various chemicals is increased, the 

 reflexes become more and more distinctive. When the chemical 

 is applied to the prostomium the reflex is always lateral — away 

 from the impinging stimulus. This is usually a right angled turn 

 in the case of "norma." stimuli. If the chemicals are much 

 stronger than this grade, two facts are noticeable. In the first 

 place, the reactions to prostommal stimulation are similar with all 

 the chemicals. This is never the case with the weaker solutions. 

 In the second place the axis of locomotion is directly reversed by 



