334 



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



have the greatest reducing power of any parts of the animal ; the 

 subumbrellar ectoderm ranks next in activity; the exumbrellar 

 ectoderm is the least active part of the animal. McClendon ('17) 

 found that the greater part of the oxygen consumption of Cassi- 

 of>ca is due to the manubrium, and that the subumbrellar surface 

 (minus the manubrium) consumes much more oxygen than the 

 exumbrellar surface plus the mesoglcea. 



2. The Electrical Gradient. The potential differences tested in 

 several species of hydrozoan medusas correspond completely to the 

 metabolic differences. The distal end of the manubrium is the 

 most negative part of the animal, the margin, including the tenta- 

 cles, is usually next, the subumbrellar surface next, while the 

 exumbrellar surface is positive to all parts of the animal. 



The forms tested were Gonionemus murbachii by Hyman at 

 Woods Hole in 1919, Lquoria victoria and Mitrocoma discoidca 

 by Bellamy in 1918 and by Hyman in 1920 at Friday Harbor, and 

 Stomotoca atra by Hyman in 1920 at Friday Harbor. The results 

 are given in Table IV. In Gonionemus the manubrium was found 



TABLE IV. 



ELECTRICAL DIFFERENCES BETWEEN MANUBRIUM, SUBUMBRELLA, EXUMBRELLA, 

 AND MARGIN OF THE BELL IN FOUR SPECIES OF HYDROZOAN MEDUSJE. 



Only two points can, of course, be compared at one time. Man., manu- 

 brium ; sub., subumbrella ; ex., exumbrella ; mar., margin ; rd., galvanometer 

 readings. Negative and positive refer to direction in the galvanometer. 



