MOVEMI'liNTS, ETC., OF FKRSH-WATKR I'].ANAE1ANS. 685 



far as mechaiiisni is coiiccinied. Cut pieces, in wliicli the 



normal mechanism for the rig-hting reaction lias been 



destroyed^ right themselves in various wa_ys, thus sliowing a 

 sort of regulation in reactions. 



IV. Electrotaxis. 



In view of the sharp and precise reactions of planarians to 

 other stimuli, it Avas thought that they would furnish excellent 

 objects for the study of electrotaxis, but unfortunately this is 

 not the case. Their reactions to the constant current are not 

 clear-cut, since the specimens become wholly or partially 

 paralysed in a very short time after the current begins to 

 act, and as a consequence the reactions become feeble and in- 

 distinct. For the sake of completeness, however, and since 

 some facts of importance are brought out, the experiments on 

 this subject will be briefly reported. 



a. Methods. — The following methods Avere used: — The 

 constant current used was obtained from the general lighting 

 circuit of the University, and reduced to the pi^oper intensity 

 by interposed resistance. This apparatus for getting the 

 current I have described fully elsewhere ( : 00, : 01), so that 

 it need not detain us here. In the circuit a rheostat was 

 inserted for regulating the strength of the current. Ordinary 

 unpolarisable brush electrodes were used. The specimens 

 were placed either in a trough with clay ends, to serve as 

 poles, and with paraffin sides of 5 mm. depth, or else on a 

 slide under a cover supported by several layers of moistened 

 filter-paper. These filter-paper ends then serve as the poles 

 of the preparation, the brushes of the electrodes being laid 

 upon them. The layer of water in Avhich the specimens Avere 

 in this sort of a preparation Avas approximately 2 '5 mm, in 

 thickness. Identical results Avere obtained by both the trough 

 and the filter-paper method, but since the latter is the neater 

 and generally more satisfactory method, it Avas used almost 

 entirely in preference to the trough, 



h. Results. — The typical result of the action of the 

 current on specimens in such a position that the long axis of 



VOL. 46, TAKT 4, — NEW SERIES. Y Y 



