THE AXIAL GRADIENTS IN HYDROZOA. 



371 



TABLE II., a, Continued. 



The tables give all of the readings which were made. There 

 have been no omissions or selection of data. Forty-two indi- 

 viduals in all w r ere tested. The first forty of these came from 

 the same lot of Tubularia, collected on December 6, and tested 

 on December 7 and 8. The last two individuals came from 

 another lot of material collected on December 8 and tested on 

 the same day. Material was kept at a temperature of 10 C. 

 A number of different readings were commonly made on each 

 stem, various levels of the stem being tested in order to obtain 

 a picture of the potential differences along the whole organism. 



The following conclusions may be drawn from the data pre- 

 sented in Tables II., a, and b: 



1. The hydranth is always electronegative to nearby regions 

 of the stem. This is shown without exception in the twenty- 

 three cases given in Table II., a. The galvanometer invariably 

 reads to the right when the hydranth is on the right electrode, 

 and to the left when the position is reversed. 



2. The difference between hydranth and distal regions of the 

 stem is greater in the case of larger hydranths and much less in 

 the case of small hydranths. Thus in nos. 2, 8, 17, and 19, 

 where small hydranths were used, the potential difference be- 

 tween hydranths and stem is 2 to 5 points of the scale; while 

 when medium or large hydranths are used, the differences are 

 much greater. These conditions are probably associated with 

 age. 



3. Hydranths are usually more negative to distal portions of 

 the stem than to more proximal regions or regions where lateral 



