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



or a posterior end of the piece. When, however, a worm is cut 

 in two immediately anterior or immediately posterior to the girdle, 

 the girdle has a lower potential than either cut end. Both these 

 regions, therefore, show a state of affairs different from that in 

 other parts of the worm. When worms were cut in two at a 

 series of points it was found that at the fifteenth segment there was 

 a change in direction of the current in twelve cases out of nine- 

 teen, and at the girdle in eight cases out of fourteen, four cases 

 in which the change was not very pronounced being included in the 

 first series, and two in the second. The change in direction of cur- 

 rent, though by no means uniform, is rather more likely to occur 

 than not, and may perhaps be connected with substances secreted 

 by the organs at these levels. 



If the distribution of potential in the earthworm resembles the 

 distribution of potential in a resting muscle, we might expect that 

 the difference of potential between the electrodes would vary ac- 

 cording to the position of the electrodes. A series of experiments 

 was tried, in which one electrode was kept stationary at a trans- 

 verse section, and the other moved along to different positions — 

 usually one near, one half way between the ends, and one on the 

 skin at the end opposite the transverse section. Great variation 

 in the deflection of the galvanometer was always observed for 

 these different positions, but it was by no means regular. The 

 most common case was that the deflection- was greatest when the 

 electrodes were near one another, decreasing as they moved away, 

 and sometimes even changing to an opposite direction when they 

 were at opposite ends of the worm. In this series of experiments 

 we have not only the complicating conditions already mentioned, 

 but also the factor of resistance which would be approximately 

 proportional to the distance between the electrodes, and if appre- 

 ciable would modify the results in the way stated. The problem 

 is one of greater complexity than that of the distribution of poten- 

 tial in the comparatively homogeneous tissue of the muscle, where 

 the resistance is small. If the earthworm were homogeneous as 

 regards electrical conductivity, and a difference of potential were 

 set up by means of a transverse section, the point of lowest poten- 

 tial would be in the middle of the cut end, and of highest potential 



