420 THE CONTRACTILE VACUOLE 



The presence of definite vacuole walls or morphological membranes 

 around the vacuoles of ciliates is not accepted by all authors. Thus, Taylor 

 (1923) believes the vacuole in Enplotes to disappear completely at sys- 

 tole, and to be replaced by an entirely new structure. If a morphological 

 membrane were present, this could hardly obtain, although Taylor was 

 able to distinguish a "highly viscous boundary" of endoplasm surround- 

 ing the vacuole. Moore (1931) was unable to cause osmication of the 

 vacuole wall in Blepharisma undid ans, using the technique of Nassonov, 

 and from this she concludes that the vacuole lacks a permanent wall. 

 This opinion was again expressed (1934) after further observation. 

 The findings of Moore are in opposition to those of Haye, who re- 

 ported thin vacuole walls in the same species. Day (1930) concludes 

 from his observations on Paramecium caudatum, Spirostomum amhi- 

 guum, and 5". teres that vacuoles in these forms are temporary structures 

 which disappear at systole. King (1935, p. 564) found that: 



The permanent components of the contractile vacuole system in Paramecium 

 multimicronucleata include the pore with its discharging tubule, and the 

 feeding canals, each made up of a distal excretory portion, an ampulla and 

 an injection tubule. . . . The membrane of the contracting vacuole is a 

 temporary structure, disappearing at systole. The pore is closed by the remnant 

 of the old vacuole which ruptures at the next systole. 



Essentially the same was found in P. aurelia. These observations were 

 made on material osmicated at 38° C. It is somewhat surprising that 

 the vacuole proper of the contractile vacuole systems in P. multimicro- 

 nucleata and P. aurelia is a temporary structure, replaced anew after each 

 contraction, whereas that of the closely related species P. caudatum is 

 commonly believed to be a permanent structure. Perhaps the stainable 

 vacuole wall described by Young for P. caudatum represents the same 

 kind of material which King believes closes the excretory pore follow- 

 ing systole in P. multimicronucleata and P. aurelia. 



After examining both living and stained material, Fortner (1926) 

 concludes that the membrane of the vacuole in Protista is a temporary 

 structure, which, after fulfilling its purpose, closes the excretory pore 

 , during the period of diastole. He further believes that all surface layers 

 sharing in the excretion process have the property of fusing together again 

 merely on contact. 



The present state of the knowledge concerning the presence or absence 



