GALVANOTROPISM OF TADPOLES. 101 



perienced excitation in all positions of the body but one ; 

 the position of least excitation, or we must even say the 

 most soothing position, is enforced upon them by that ex- 

 perience. Stroking the wrong way excites them, they 

 therefore avoid the positions in which that happens. 

 Stroking the right way pacifies them, and they therefore 

 adopt the positions in which that is best received. 



GALVANOTROPISM. 



In the lowest forms of animal life — amoebae, infusoria, 

 etc. — the polar response to excitation by the constant cur- 

 rent is diametrically opposed to that obtaining upon dif- 

 ferentiated muscle and nerve. Whereas upon the latter 

 the make excitation is kathodic, and the break excitation 

 anodic, upon non-fibrillated protoplasm the make excitation 

 is anodic and the break excitation kathodic. With these 

 effects there is in many cases a remarkable orientation in 

 relation to the current — " galvanotropism " — accompanied 

 in some instances by an evident disintegration of protoplasm 

 on the anodic side {e.g., in Actinosphcerium and in Pelomyxa), 

 in others {e.g., in Paramcecium), by amoeboid or swimming 

 movements in the direction of the current, i.e., away from 

 the anode. In general the orientation of Infusoria is such 

 that they arrange themselves longitudinally in the lines of 

 current with their anterior ends towards the kathode, and 

 their swimming movements, if any, in that direction {e.g., 

 Paramcecium) ; in some instances {e.g., Polytoma uvella, 

 Cryptomonas erosa), the orientation is reversed ; in others 

 again it is transverse, the long axis of the animal disposing 

 itself at right angles to the current (Verworn). 



Fertilised frog's eggs exhibit according to Roux very 

 remarkable galvanotropic effects ; in a layer of spawn 

 traversed by strong alternating currents (ioo volts), each 

 individual egg presents at the end of a few minutes a division 

 into three zones — two dark polar areae separated by a light 

 equatorial zone— and the eggs collectively dispose them- 

 selves in conformity with the lines of current-diffusion so 

 that the light equatorial stripes lie at right angles to the lines 



