424 THE CONTRACTILE VACUOLE 



that the vacuole removes approximately ten times as much water as is 

 taken in with food, a fact which he fails to correlate with his claim of a 

 predominantly excretory function. Day (1927) suggests that vacuoles in 

 Amoeba originate in "the fusion and coalescence of ultramiscroscopic 

 droplets of soluble katabolic waste which may include water of osmosis." 

 He observed that conductivity water increases size, number, and pulsation 

 frequency of vacuoles. Essentially the same observations and conclusions 

 were extended by him to Faramecuim and Spirostomum (1930). Mac- 

 Lennan (1933) observed in the Ophryoscolecidae that granules accumu- 

 late around the vacuole during the early part of diastole and then are 

 gradually reduced in number. The formation of accessory vacuoles in 

 these granular regions involves a solution of granules in the vacuolar 

 fluid. He suggests this as a possible method for the elimination of kata- 

 bolic wastes. Since he found the pellicle of these organisms to be rela- 

 tively impermeable, MacLennan believes an excretory function to be all 

 the more probable in these forms, since the vacuole is the only visible 

 means for the removal of wastes. Adolph (1926) found that no change 

 of external conditions alters significantly the rate of elimination of fluid 

 by vacuoles of Amoeba, and from this concludes that water is not elimi- 

 nated merely because it has unavoidably difl'used into the body. 



Dimitrowa (1928) observed (as mentioned earlier) that mechanical 

 interference, as by pressure on the cover glass, induces the development 

 of extra vacuole systems in Varamechan. In most instances these vacuoles 

 assumed normal structure, size, and pulsation frequency, although in some 

 cases there were actively pulsating vacuoles with no radial canals. Dimit- 

 rowa explained the formation of extra vacuoles, as well as of those nor- 

 mally formed at fission, by the assumption that if for one reason or an- 

 other the excretory organs become inadequate to remove wastes, extra 

 organs are formed. If one vacuole is rendered ineffective by mechanical 

 interference, then another is formed to take over its function. Likewise, 

 since metabolism is thought to be increased during fission, new vacuoles 

 are formed to care for the increased production of wastes. Extra vacuoles, 

 induced artificially, obviate the necessity for the formation of a like 

 number at fission, since an ample excretory function is already present. 



Somewhat contradictory evidence has been presented by various authors 

 concerning the nature of nitrogenous end products of metabolism in the 

 Protozoa. As previously mentioned, Griffiths (1888) reported uric acid 



