544 



Prof. A. B. Macallum. Acineta tuberosa : [Feb. 19, 



The only other source of the potassium in the condensations in the 

 tentacles is the potassium of the material absorbed as food through the 

 tentacles. The organisms which are the prey of marine Acinetce are chiefly 

 vegetable and the cytoplasm of these is charged with potassium which, with 

 their other constituents, is absorbed through the tentacles. Sometimes, 

 indeed, such organisms heavily impregnated with potassium may be found 

 attached to the tentacles of an Acineta. 



The potassium absorbed seems to play no part in digestion or metabolism 

 and though its condensation in the superficial films of the tentacles would 

 indicate that it lowers their surface tension this diminution is not dependent 

 wholly on its presence. The fresh-water form Podophrya (Tocophrya) 

 quadripartita, which grows attached to Cladophora, Vaucheria, and other 

 Confervoid forms, does not contain any potassium even when it is absorbing 

 material from its prey. It does not become impregnated, even in the 

 slightest degree, with potassium salts when it is placed in sea water for 

 24 hours. It is manifest, therefore, that the tentacles and the general 

 surface of these organisms are ordinarily impermeable to the salts of their 

 medium. 



The low surface tension on the tentacles of Acineta, and at the points on 

 the hillocks where the tentacles arise, is doubtless due to formation in these 

 structures of a substance derived from the metabolism of the proteins and 

 other constituents of the cytoplasm. When potassium salts are present they 

 may co-operate with it in its action on the surface tension. What this 

 substance is cannot definitely be indicated and conjecture is our only 

 resource. On first consideration a lipoid is suggested. To determine whether 

 such a body is present in sufficient quantity to permit it to be distinctly 

 shown under the microscope, preparations of active Acinetce hardened in 

 4-per-cent. formol were treated with a saturated solution of scarlet red in 

 70-per-cent. alcohol for 2 hours and after being washed for a few minutes in 

 60-per-cent. alcohol and then in distilled water, were mounted in 50-per-cent.. 

 glycerine. A careful examination of such preparations under the microscope 

 revealed minute spherules of fat in the membranes of the tentacles. In 

 some examples of Acineta these spherules were very numerous, in others 

 they were few. Occasionally a distribution of fat like that shown in fig. 7 

 was observed. In such the superficial membrane of the terminal capitate 

 end of the tentacle was deeply impregnated with fat or it presented the 

 appearance of a mosaic formed of closely placed very minute spherules of 

 fat. The superficial membrane, however, in the vast majority of the tentacles 

 gave no indication of fat uniformly s diffused throughout it. 



Scarlet red is not a staining reagent to demonstrate the occurrence of 



