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



dence of this by means of the galvanometer. If this relation 

 should be found to exist, there is a further opportunity of test- 

 ing the validity of the conclusion in the case of axial heteromor- 

 phosis. For this reason we selected the earthworm for our study, 

 since in the earthworm it had been shown by one of us that there 

 regenerates from the anterior cut surface of posterior pieces not a 

 head, but a tail. We should expect to find under these circum- 

 stances a reversal of the potential in this region,* when compared 

 with an anterior cut surface in the more anterior regions of the 

 worm. The following pages give the results of our examination. 



METHODS. 



Both Lumbricus terrestris and Allolobophora foetida were used. 

 Since the results appeared to be similar for both species, Lum- 

 bricus, being larger and showing on the whole greater differences 

 of potential, was preferred when available. In all, sixty-four 

 worms were used, the number of tests made upon any one varying 

 from one to seventeen. Differences of potential were detected by 

 a Rowland-d'Arsonval galvanometer, connected with a pair of 

 non-polarizable electrodes. Since the regulation of these electrodes 

 was found to be troublesome, and since they were liable to intro- 

 duce a source of error into the readings, their manufacture and 

 regulation had best be described. Two glass tubes about three 

 inches long, somewhat smaller at one end, were plugged at the 

 small end with kaolin or filter paper, moistened with normal 

 (0.85%) salt solution. The plug extended about a half Inch be- 

 yond the end of the glass tube. When made of kaolin, the end, 

 after being used, could be easily broken off and re-formed from 

 fresh material. When made of filter-paper, the tip, if it became 

 contaminated from touching the worm, could be cut off. Above 

 the plug each tube contained a saturated solution of zinc sulphate, 

 into which projected through a cork a small amalgamated zinc 

 electrode, connected by a wire with one of the poles of the gal- 

 vanometer. Since the instrument was so sensitive that the slight- 

 est loss of equilibrium was at once registered by a deflection of the 

 mirror, great care had to be exercised in keeping the junctions of 

 wires and zinc electrodes dry, and in balancing the other elements 



