698 IJAVMONO PKARL. 



iiioi'e firmly to the substrate. Weaker currents caused no 

 effect whatever. I was inclined to believe that the longitu- 

 dinal contraction and the gripping of the bottom were the 

 only rheotactic reactions which the organism exhibited. It 

 was found later, however, that there was a very precise 

 rheotactic reaction of a diff(>rent character. In the course 

 of the experiments on reactions to localised chemical stimuli 

 by the capillary tube method, it was discovered that by using 

 a tube with a relatively large opening (from ^ to h nnii. in- 

 diameter) and letting the ordinary- tap-water in which the 

 animals were flow out of it, by its own weight, a current of 

 just the right intensity to cause a positive reaction could be 

 produced. The animals would tuni very sharply towards the 

 source of such a current, the reaction being evidently the 

 same as that given to other Aveak .stimuli (chemical and 

 mechanical). This reaction is localised in the same way as 

 the usual ]iositive reaction. It is given only when the current 

 is directed against the head or anterior part of the body. 



It is thus seen that the planarian is positively rheotactic to 

 very weak currents, the form of the reaction being precisely 

 the same as that given to other weak stimuli. It seems very 

 doubtful if this reaction is of any importance in the normal 

 activity of the animal. 



G. General Summary and Discussion of Results. 

 As was stated earlier in the iiaper, the problem with which 

 this study deals is the analysis of the behaviour of the 

 common fresh-water planarian. The movements and reac- 

 tions to all the UKH-e important stimuli, with the exception of 

 light and heat, have been described and analysed into theii- 

 component factors in the body of the paper. It is beli(>ved 

 that it is of the greatest importance to have as conipleti> and 

 detailed an account of the various activities as possible, and 

 as a consequence full details hav(> been given in the case of 

 each suljject treated. Sin('(> this method of treatment 

 necessarily makes \]w account of considerable length, it has 

 a tendency to obscuiv the general and significant results in a 



