418 THE CONTRACTILE VACUOLE 



side. Calculations have been made of the physical force necessarily ex- 

 erted by the amoeba to accomplish this, but they have not taken into 

 account some of the properties of physiological membranes, such as spon- 

 taneous disintegration when membrane comes into direct contact with 

 membrane. The adherence of conjugating organisms may be dependent, 

 likewise, on these same properties of membranes. While it is interesting 

 to speculate on such matters, it must be admitted that these remarks on 

 feeding amoebae are purely speculative, with little other than superficial 

 observation to support them. 



Concerning the presence of a permanent (morphological) membrane 

 surrounding the contractile vacuole, there are diverse opinions. These 

 diverse opinions apply not only to different species but even to the same 

 species. Howland (1924a) found that the contributory globules as well 

 as the vacuole may be removed from the organism to the surrounding 

 water, where they retain their identity for an indefinite period of time. 

 This may be taken to indicate a considerable degree of permanence of the 

 vacuole wall, such as would be possessed by a morphological membrane, 

 although Howland is of the opinion that these vacuole membranes are 

 temporary. A temporary physiological membrane, formed of oriented 

 molecules in a compact layer, may be expected to retain its identity for 

 an appreciable period of time before dispersion of the molecules occurs, 

 but it hardly seems probable that this "appreciable period of time" can 

 be more than a few minutes. Day (1927) expresses the opinion that the 

 vacuole wall in A. proteus is a "condensation membrane," or gel, disap- 

 pearing with each contraction. By "condensation membrane" Day very 

 likely implies such a structure as has been described above as a physiologi- 

 cal membrane, so that the two terms may be taken as synonymous. Con- 

 cerning A. proteus, Mast (1938, p. 307) states: "At the surface of the 

 contractile vacuole under the layer of substance containing the beta gran- 

 ules, there is a layer or membrane about 0.5 micron thick which is opti- 

 cally well differentiated from the adjoining substance on either surface, 

 for under favorable conditions a line indicating an interface can be clearly 

 seen at both these surfaces." Whether this membrane is a permanent 

 structure or is formed anew with each successive vacuole was not sug- 

 gested by Mast. After an examination of fixed, stained, and sectioned 

 material, Haye (1930) concluded that vacuole membranes are lacking 

 in Amoeba, although it is probable that this author referred to morpho- 



