THE AXIAL GRADIENTS IN HYDROZOA. 373 



branches are present. This is shown in numbers 3, 5, 6, 8, 10, 

 15, 16, 18, 37, and 40, Table II., a. Thus for example, in no. 3, 

 the difference between the hydranth and the distal stem is 15 

 divisions of the scale in the first trial, 12 in the second, while the 

 difference between the same hydranth and a more proximal region 

 of the stem where a lateral branch was present was 8 divisions in 

 both trials. In one case, no. 13, the region of branching was 

 negative to the hydranth; in another case, no. 39, there was 

 practically no potential difference between the hydranth and 

 the branching region. We therefore see that proximal regions 

 of the stem are more negative than distal, especially when they 

 bear branches. This is due to the fact that the hydranth domi- 

 nates only a certain length of stem, and beyond that length 

 physiological isolation has occurred with the formation of a 

 new individual, expressed by the development of lateral branches. 

 Such new individuals like the original one are electrically negative 

 apically. 



4. Distal regions of the stem are nearly always electronegative 

 to nearby proximal regions. This was the case in 14 of the 17 

 cases tested in Table II., b. In two cases, nos. 28 and 34, there 

 was no potential difference between two such regions of the stem; 

 in one case, no. 13, the gradient was reversed, the distal region 

 being positive to the proximal region. Such cases as these three 

 account for the fact that occasionally, distal and proximal pieces 

 of the stem regenerate simultaneously, or that the proximal piece 

 may precede. 



5. The potential difference between distal and proximal regions 

 of the stem is always very much less than that between hydranth 

 and distal regions of the stem. 



6. The potential difference is usually slight or absent or may 

 be reversed between distal regions of the stem and far proximal 

 regions, or regions bearing branches. Of six cases tested, two 

 showed no potential difference (nos. 4 and 33, Table II., b); 

 in one case, the distal region was negative (no. i); and in the 

 other three cases, the far proximal region or branching region 

 was negative to the distal region (nos. 9, 25, 36). This verifies 

 what was said in paragraph 3. These far proximal regions are 

 really beginnings of new individuals and hence are more electro- 

 negative than the regions immediately distal to them. 



