82 



THE AMERICAN MONTHLY 



[March, 



II. Rest Period of Vesicle : Average Time, ^ Second. 



Movements. — Vorhofe begins to contract. 

 Position. — Vorhofe in same position. 

 Canals in same position. 



III. Diastole of Vesicle : Average Time, 59 Seconds. 



Movements. — Vesicle expands suddenly at first, then slowly. 



Vorhofe contracts at first and then slowly expands. 

 Position. — Vesicle expands from a central point. 



Vorhofe in same position. 



Canals in same position. 



Enough has been said concerning the general structure of the 

 contractile vesicle ; let us now turn our attention to its probable 

 function. In the first place, it should be determined whether 

 the content of the vesicle is a gas or a liquid. I am quite fully 



Explanation of the Figure. 



Parainecium aurelia. 



c. v., contractile vesicle in diastole, v. s., vesicular systole. 



Vh., Voi'hofe. c, canals, n., nucleus, o.. oesophagus, es., 



ectosarc. en. s., endosarc. f. b., food vacuoles, f. b., food 



bolus in process of formation. 



convinced that it is a gas, because microscopically it gives the 

 appearance of a gas bubble suspended in a liquid or a semi-liquid, 

 I have tried various stains and in no case was the contents of the 

 vesicle stained, either before or after the death of the Parame- 

 cium. If there were a liquid it would certainlv be stained after 

 the death of the animal if not during life. I have also often 

 noticed that when the organism slowly died the vesicle enlarged 

 to such an extent as to rupture the cell-wall and allow the con- 

 tents of the vesicle to protrude as a gas bubble which was fin^illy 

 absorbed by the water. The comjjosition ofthisgasis not known. 

 It is probably a gas fornied by metabolic processes going on in the 

 living; organism. 



