STIMULI AND THEIR ACTIONS 



459 



the current be reversed, so that the previous anode becomes the 

 kathode, and vice versa, the two crowds of Infusoria rush toward 

 one another like two hostile armies, cross and again assemble at 

 the opposite poles. There are few physiological experiments that 



FIG. 234. Galvanotaxis of Polytoma uvella. A, Resting quietly ; , swimming toward the anodu 

 after the making of the constant current. 



are so pleasing and graceful as the galvanotactic dance of the 

 Infusoria. 



A third form of galvanotaxis is shown by the ciliate infusorian 

 Spirostomum ambiguum. 1 If these elongated Infusoria, which can 

 be perceived even with the naked eye as small white fibres c. 2 mm. 

 in length, be placed in water between parallel clay-electrodes, it is 

 seen that upon the making of the constant current they draw 

 together suddenly by the sudden contraction of their myoid-fibres, 

 but do not, as might perhaps be expected, swim toward one or the 

 other pole. Instead of this, by means of their ciliary motion 

 accompanied by much bending of the body, they gradually turn so 



FIG. 235. Galvanotaxis of Spirostomum ambiguum. After the making of the current the Infusoria 

 place themselves with their long axis at right angles to the direction of the current 



that their long axes are at right angles to the direction of the 

 current, and maintain this position, although constantly bending 

 and twitching their long bodies (Fig. 235). This form of gal- 

 vanotaxis may be termed transverse. In other organisms trans- 

 1 Cf. Verworn ('92, '96). 



