336 T. H. Morgan and Abigail C. Dimon. 



current, the other half agreeing with this experiment in showing 

 no reversal. 



From experiments i and 2 it may be assumed that when an 

 earthworm is cut in two, the transverse section commonly repre- 

 sents a point of lower potential than the uninjured surface near to 

 it. At the cut end chemical changes no doubt take place as a re- 

 sult of the fluids there set free, and of the general breaking down 

 of tissues. These conditions might be expected to alter the elec- 

 trical potential at the cut end, and presumably, where these changes 

 are greatest, the alteration of potential will be greatest. Since, 

 however, the transverse section is usually lower in potential than 

 the uninjured surface near it, whether the section be at the anterior 

 or posterior end of the piece, the difference in potential cannot bear 

 any relation to the kind of regeneration that is to take place. 



Having illustrated the more regular and more usual conditions 

 of distribution of potential between surface and cross section, two 

 illustrations of the exceptions to this condition, sometimes met 

 with, will now be given. In the first a distribution of potential 

 different from the average occurred throughout the whole worm. 

 In the second, a short piece of a worm showed unusual conditions. 



Experiment 3. Lumbricus terrestris, young. Cut end posterior. 

 The zero point of the galvanometer was 27.4, and the electrodes 

 deflected it to 26.3 at the beginning of this experiment, and to 28.9 

 at the beginning of the next experiment made that day. Some 

 doubt may, therefore, be thrown on two of the readings given 

 below — those at the girdle and at the fifteenth segment. The direc- 

 tion of deflection in these cases is probably correct, but the amount 

 is small. The readings were as follows :- 



Posterior to middle a 24.0 Surface positive 



Just back of girdle b 29.0 " " 



A .^ • ^ • J, ( c 33. c Cut end positive 



Anterior to girdle 3 -^-^ -i ^ ^^ 



] d 34.6 



At 15th segment. e 26.5 Surface positive 



I f 32.8 Cut end positive 



Anterior to icth segment ' ? ^o-O 



^ ' h 34.9 



i 35-0 



