656 RAYMOND PEAEL. 



seen that tins organ bent directly towards the mouth of the 

 capillary. The pharynx oriented itself with reference to the 

 issuing chemical. 



The cases in which specimens were "indifferent" to this 

 solution (i.e. did not give either the positive or negative re- 

 action) were evidently not due to the fact that the animal 

 was not stimulated^ hul, on the contrary, that it was stimu- 

 lated about equally to negative and positive responses. This 

 was indicated by their restless behaviour when " indifferent." 

 While the animal as a Avhole moves in a straight line, the 

 head constantly moves slightly towards and away from the 

 stimulus. Evidently the solution is not quite strong enough 

 to induce a definite negative reaction, nor quite weak enough 

 to cause a clear positive response. 



■^jj- per cent., j\j- per cent., and -^j^ per cent. — Distinct posi- 

 tive reaction in all cases. 



-jjrjj per cent. — Positive reactions in some cases, mainly 

 indifferent. The " indifference " is now due to lack of 

 stimulation. 



Below yiy- per cent. I have been unable to get definite 

 responses of any sort with KOI. 



Magnesium Chloride, i per cent. — Usually sharp 

 negative reaction. In some cases a slight turn towards the 

 stimulus preceded the negative response, nnd in some few 

 other trials the aniaial was indifferent. 



-i- per cent. — Weaker negative reaction. In one case 

 clear positive reaction. No local contraction of the region 

 stimulated is caused by this chemical. 



Jy per cent. — Positive reaction in all cases. Complete 

 food reaction could be induced. 



_i_- per cent. — Weak positive reaction or indifferent. 



Summary. — To the salts NaCl, NaBr, KCl, and MgCU 

 the planarians react as to other chemicals, by giving the 

 negative response to strong concentrations and the positive 

 to weak. 



Cane-sugar, — Sugar solutions, in all concentrations 

 above j^ per cent., so far as I have been able to discover. 



