1913.] A Study on the Action of Surface Tension. 541 



is sometimes observable between the crystals in the surface film of the head 

 of the tentacle. 



The potassium salt is more abundant in the capitate portion of the tentacle 

 than elsewhere in the latter. 



Contraction of the tentacles is rarely observed in specimens very recently 

 taken from their habitat, but when it is developing the potassium salt 

 diffuses from the surface films of the tentacles into the axial portions, and in 

 consequence in such, when treated to reveal the potassium, the tentacles are 

 black throughout (fig. 4). In certain of such preparations the cytoplasm of 

 each hillock and of the immediately underlying part has also a dark shade 

 which indicates that the potassium salt, as a result of the retraction, has 

 begun to diffuse from the tentacles downward into the cytoplasm. When 

 the tentacles are completely retracted the potassium is then diffused 

 throughout the hillocks into which they are withdrawn and also downward 

 into the underlying cytoplasm. In some specimens even the hillocks may be 

 inverted and then one finds their outline marked out by the deep black 

 reaction they give. In fig. 5, which represents this occurrence, a more 

 marked diffusion downward into the cytoplasm is shown by the dark shade 

 which becomes less and less marked the further downwards this diffusion 

 proceeds. As this diffusion develops the potassium salts tend to condense 

 more on the surface of the spherules than was the case when the tentacles 

 were still extended, especially on those spherules which are found in the 

 anterior half of the organism. This may be explained as due to the greater 

 concentration of potassium salts in the surrounding cytoplasm in this region. 



Occasionally in specimens one observes crystalline bodies of unknown 

 composition in the cytoplasm, on the surface of which potassium salts may 

 be condensed. The condensation on their surfaces has been observed to be 

 more pronounced when the tentacles are partially or wholly retracted (fig. 5). 



The salt of potassium most abundant in these condensations is probably 

 the chloride. Tins was shown by the silver reaction. When living Acinetce 

 were placed for 30 minutes in N/10 solution of silver nitrate, to which some 

 nitric acid was added, and afterwards exposed to bright sunlight for 

 10 minutes, a brown-black deposit of the reduced silver chloride was found 

 in them only in the superficial films of the tentacles and at the germ-bud- 

 cytoplasm interface, where the potassium reaction was obtained. This would 

 seem to indicate that the potassium is present as chloride only, but as the 

 reaction for the SO4 ©f sulphates was, unfortunately, not applied one must 

 admit the possibility of some of the potassium being present as sulphate. If, 

 further, sodium, calcium, and magnesium, as chlorides, are present in these 

 organisms they must undergo condensation on the same surfaces and 



