146 



ELECTRICITY AND PROTOPLASM 



[Ch. VI 



end towards the anode. Since n is here supposed to be less 

 than X, the resultant effect is to move the animal forward. In 

 moving forward in its spiral course, one side becomes presented 

 to the anode. On this side the excess of energy of the stroke 

 is a; + m, while on the kathode side it is 2; — n. The resultant 

 effect of the cilia on the two sides forms a couple which revolves 

 the organism about one of its short axes until it comes again 

 into the axis of the current, but with its anterior end towards 

 the kathode. The beating of its cilia must now carry it towards 

 the kathode (Fig. 39). 



Fig. 39. — Diagram showing the successive attitudes (a, 6, c, d, and e) assumed by 

 Paramecium when its head is turned towards the anode at the beginning (a). It 

 rotates till its head is next the kathode (e) . (From Lxtdlofp, '95.) 



Before leaving the Protozoa, we ought to look over the whole 

 field. We have hitherto considered only cases of migration 

 towards the kathode — negative galvanotaxis. Vekwoen 

 ('89''), however, has found that some Protista are positively 

 electrotactic ; namely, the flagellata, Polytoma uvella, Crypto- 

 monas ovata, and Chilomonas Paramecium ; the ciliate, Opalina; 

 and some bacteria. Finally, Veewoen ('96, p. 446) describes 

 one of the elongated Ciliata- — Spirostomum ambiguum — which 

 places its long axis across that of the current and migrates 

 towards neither pole, a condition which may be called (after 

 Vbrwoen) transverse electrotaxis. 



Passing now to the Metazoa, we find investigations concern- 

 ing electrotaxis among Invertebrates by Nagel ('92 and '92' 



