THE AXIAL GRADIENTS IN HYDROZOA. 367 



nese dioxide being formed. It was found by Child that this 

 capacity of organisms to reduce permanganate exhibits the same 

 kind of a gradation in relation to the body axes as does their 

 time of death in toxic solutions. The apical ends reduce the most 

 permanganate and take on a very deep brown or almost black 

 color and the depth of this color decreases basipetally. 



I have observed the staining of Tubidaria by potassium per- 

 manganate. The picture thus presented is identical with the 

 course of disintegration already described. The tips of the 

 proximal tentacles stain first, the tips of the distal tentacles next; 

 the stain progresses rapidly down the tentacles (on the outer 

 surfaces of the proximal tentacles before their inner surfaces) to 

 their bases. Meantime the stain appears on the distal end of 

 the body of the hydranth and progresses basipetally along its 

 ectoderm. After the staining is completed, it is found that the 

 tips of both sets of tentacles and the mouth region of the hydranth 

 are very deeply stained and the stain shades off to the bases of 

 tentacles and hydranth. This was best observed by turning the 

 hydranth with a needle so that it faced upward. 



The staining of the stem was naturally difficult to observe. 

 The short stalk below the hydranth became stained soon after 

 the hydranth but the staining of the stem proper was very slow. 

 As far as could be observed the stain proceeded from the distal 

 end of the stem proximally. The observations were, however, 

 unsatisfactory. 



The younger hydranths stain much more rapidly than the 

 larger ones, but exhibit less distinct graded differences between 

 different regions of the hydranth. 



D. ELECTRICAL GRADIENTS IN TUBULARIA. 

 Differences in electrical potential along the axes of organisms 

 form still another manifestation of the metabolic gradients and 

 are at present being investigated by members of this laboratory 

 for a number of the lower forms. These electrical gradients 

 correspond in all respects to the death and staining gradients. 

 The regions of highest susceptibility and reducing power are 

 electronegative (galvanometrically) to regions of lower suscepti- 

 bility and reducing power. This matter has been discussed 



