666 



EAYMOND PEARL. 



passing either from the water to the sugar or vice versa. 

 When in sugar solution it gives a positive reaction to tap 

 water, whether applied by the capillary tube method or as just 

 described. It is evident, from this experiment, that collec- 

 tions are not formed by planarians in the same way that they 

 are by Infusoria. The animals are not negative to the 

 surrounding water after they have been in the solution. To 

 test and verify this conclusiou the experiment was repeated 

 with solutions of diiferent substances. It was found that in 

 case of all substances in concentrations to which the animals 

 gave a positive response when stimulated by the capillary 

 method, the specimens would pass back and forth from water 

 to solution and vice versTi, indifferently. If solutions were 

 used in concentrations to which a negative reaction was given 



Fig. 34. — Diat^ram showing the arrangement of " two-drop " experi- 

 ment with chemicals. 



when stimulation was by the capillary method, the specimens 

 merely stayed in the water drop. When they came to the 

 boundary line of the strong solution they gave the negative 

 reaction, and hence stayed in the water. This immediately 

 raises the question, why would there not be a permanent 

 collection of the planarians formed in a drop of^ a substance 

 to which they give the positive reaction, provided they were 

 First put in a drop of some substance to which they were 

 strongly negative ? There is evidently no theoretical reason 

 why this should not take place, but there is an important 

 practical one. This is that any solution which would cause a 

 negative reaction, under these circumstances, will, so far as I 

 have found, also seriously modify the animals' movements, if 



