THE CONTRACTILE VACUOLE 413 



to exist in some amoebae, may be the site of origin of new vacuoles when 

 the function of the original vacuole is disturbed by artificial means or 

 removed by operation. While such granules have not been demonstrated 

 to be scattered about in the cytoplasm of P. caudatum, their presence 

 would explain the origin of extra vacuoles in this form, when func- 

 tion of the original vacuoles is interfered with mechanically, as reported 

 by Dimitrowa. The origin of new vacuoles at fission would have a similar 

 explanation, since, as proposed by Dimitrowa, during fission the greater | 

 abundance of metabolites would impose a necessity on the organism 

 essentially similar to interference with normal function. After fission, 

 when the daughter cells are smaller than the parent cell was immediately 

 prior to fission, and the metabolic rate is lowered, there no longer exists 

 a stimulus for the formation of extra vacuoles, and the daughter cells 

 appear quite normal, with the usual number. 



The Structure of Contractile Vacuoles 



The question of the structure of the contractile vacuole and its as- 

 sociated parts has occupied the attention of protozoologists for many 

 years. As a result the main question has been broken up into several 

 parts, each concerned with a limited phase of this main question. Is the > 

 vacuole surrounded by a permanent membrane? Is its discharge to the y 

 exterior through a permanent excretory pore? If there is no permanent 

 pore, how may one explain the formation even of a temporary pore, and 

 once formed how is it closed again? Is the vacuole a permanent structure, - 

 or does it arise anew at the beginning of each new cycle? 



The dispute as to the presence or absence of a permanent membrane 

 surrounding the vacuole began over a hundred years ago, and continues, 

 with little to indicate that is will end within the near future. According 

 to Taylor (1923), to whom we may refer for a more detailed account 

 of the history of this question, the following investigators have written 

 in support of the idea of a permanent membrane: Ehrenberg, Siebold, 

 Claparede, Lachmann, Degen, and Stempell. Those who believe that 

 the vacuole possesses no permanent wall are: Dujardin, Meyen, Stein, 

 Wrzesniowski, Perty, Schmidt, Zenker, Maupas, Rhumbler, Biitschli, Lan- 

 kester, and Khainsky. Taylor himself holds this view, at least for Eu- 

 plotes. Without reflecting unfavorably in any way on the researches of 

 those who worked on this subject prior to 1900, or possibly as late as 



