540 



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



dissolved. In both cases there would be a condensation of potassium salts 

 from the enclosing or surrounding medium on, but not in, the surface of the 

 enclosed object or system. 



Some portion, however, of the potassium salts found to occur at the inter- 

 face between the maternal and germinal cytoplasms must be explained as 

 involved in the process of excretion. In the canaliculus connecting the 

 germinal cavity and the exterior potassium salts are frequently found 

 (figs. 3, 4) and these may extend in the form of a plug or mass through the 

 pore in the lorica. Sometimes the salts so excreted do not reach the exterior, 

 for if the external end of the canaliculus is not in line with the pore in the 

 lorica the salts pass to the right and left in the grooves above the cytoplasm 

 formed by the two parallel folds of the lorica. The position of these folds and 

 the presence of potassium salts in them is shown in fig. 9, which represents 

 a specimen as seen when its anterior surface is turned towards the observer. 

 Even when the canaliculus is flush with the pore in the lorica potassium salts 

 may be found in the groove for some distance to the right and the left of the 

 pore (fig. 3, a). 



The occurrence of potassium salts at the interface formed by the cytoplasm 

 and each of the included spherules can be demonstrated only in a few 

 specimens of Acineta and even when the demonstration is clearest it is never- 

 theless of such a character as to escape observation unless it is specially 

 examined with that end in view. That there should be such a surface con- 

 densation of potassium salts in the cytoplasm on the surface of the spherules 

 would follow from the fact that the spherules must have a different surface 

 tension from that of the cytoplasm. Why this condensation is not evident in 

 every specimen of Acineta cannot be explained unless it be that the surface 

 tension of the cytoplasm at the cytoplasm-spherule interfaces is not, in the 

 majority of Acinetcc, diminished as it is in the cytoplasm immediately 

 adjacent to the germinal bud or in the surface film of the tentacles, in which 

 case there would be little condensation of potassium at the cytoplasm- 

 spherule interfaces. 



The condensation in the tentacles is sharply confined to their surface films. 

 This is shown particularly in fig. 6, representing the terminal portions of two 

 tentacles greatly magnified. The coarse granules there revealed represent 

 the crystals of the hexanitrite of cobalt, sodium, and potassium, blackened 

 by ammonium sulphide. The crystalline deposit appears to be very 

 voluminous but this is due to the fact that potassium forms only about 

 16 per cent, of the crystals themselves. Were, however, the potassium much 

 less abundant than this 'the precipitate would not be crystalline but one 

 finely diffused throughout the surface film. Such a finely diffused precipitate 



