328 L. H. HYMAN AND A. W. BELLAMY. 



first and more deeply, and the depth of color diminishing along the 

 axis. The staining gradient was most marked in medium-sized 

 individuals, practically absent in large or small individuals ; the 

 latter, however, stain more deeply than larger individuals. Child 

 has also noted a staining gradient in potassium permanganate in a 

 Grantia-like sponge at Friday Harbor. 



From these observations it may be concluded that there is a 

 metabolic gradient along the axis of these simple sponges, the 

 oscular end having the greatest metabolic activity and this activity 

 decreasing along the axis. 



2. The Electrical Gradient. Numerous tests of the potential 

 difference along the axis of Lcitcosolenia and Grantia showed that 

 in the great majority of individuals the oscular end is electro- 

 negative (galv.) to the basal end. In some cases, usually in small 

 or very large individuals, there was no potential difference along 

 the axis ; in a few cases the potential difference was reversed, the 

 oscular end being positive (galv.). The results are given in Table 

 I. The potential differences are rather small. 



Certain facts not presentable in the table were also noted. In 

 large specimens there is likely to be a greater potential difference 

 between the oscular end and the middle of the sponge than between 

 the oscular and basal ends, indicating some degree of physiological 

 independence of the basal region in such large specimens. There 

 is usually no potential difference between lateral branches (Leuco- 

 solenia) and the main osculum i.e., the buds are also negative 

 (galv.). Freshly cut cross-sections (Grantia) are markedly nega- 

 tive (galv.), being often negative even to the oscular end; this is. 

 of course, merely an example of the current of injury. 



In these sponges, then, is found the usual correspondence be- 

 tween metabolic rate and electric potential, the region of highest 

 metabolic rate being electronegative (galv.). 



IV. HYDROIDS. 



The work on the electrical gradients of hydroids was done by 

 Hyman at Woods Hole in the summer of 1919, with the exception 

 of the data on Obelia borcalis, which were obtained by Bellamy in 

 1918 at Friday Harbor. 



i. The Metabolic Gradient. The metabolic gradients of several 



