24 MARY DRUSILLA FLATHER. 



The theory of Haeckel (10) that the pulsating vacuoles are 

 Ived from the simple food vacuoles was questioned by Maupas 

 , who declared that the two vacuoles have but one characti r- 

 i-tic in common, the absence of a true limiting membrane. 

 In all other characteristics they differ completely. The fluid 

 content of the contractile vacuole contains the soluble waste 

 products of metabolism, while that of the food vacuole is a plasma 

 or cellulose sugar in which digestion can take place. According 

 to Maupas (20) the contractile vacuole is a special physiological 

 adaptation of the protoplasm and does not depend phylogeneti- 

 cally upon any other structure. 



Opinions are even more contradictory in regard to the special 

 function of the vacuole. Hartog (12) and later Stempcll (28) 

 emphasized the importance of the vacuole as an adjuster of 

 osmotic equilibrium. It is a physical necessity to the naked cell 

 living in water since it prevents overdilution and ultimate 

 destruction of the protoplasm. Others ascribed to the vacuole 

 the additional functions of circulation, respiration, and excretion. 

 No one can doubt its assistance in general circulation. Kent 

 (16) mentioned that Lieberkuhn, Claperede and Lachmann even 

 considered it a rudimentary heart. In respiration it serves 

 according to Haeckel (10), Maupas (20), Butschli (3), Ehrmann 

 (8) and Stempell (28) merely as an agent to remove the end 

 products of oxidation. The fluid which accumulates in the 

 vacuole has previously circulated through the organism, and 

 must therefore have lost the feeble quantity of oxygen which it 

 held in solution on entering the protoplasm through the gullet or 

 the periphery. The vacuole may be said to receive all the soluble 

 end products of general metabolism. Schmidt (16) fcfimd the 

 vacuole comparable in function to the renal organs of higher 

 animals, especially the excretory water canals of Turbellaria. 



Rossbach (24) first showed conclusively that the rhythm and 

 size of the vacuole vary with the physical and chemical properties 

 of the surrounding medium. Since then a considerable amount 

 of work has been done on the physiology of these primitive or- 

 gans. The pulse frequency, or the number of seconds elapsing 

 between two successive pulsations presents under normal con- 

 ditions a constant average among individuals of the same race. 



