THE CONTRACTILE VACUOLE 441 



form for the protozoan Golgi apparatus is that of granules, globules, 

 or short rods. Overimpregnation of a granular region, which occurs when 

 the process is carried out at too high temperatures, has been shown to 

 produce heavy black bands, or rings, in certain organisms. This fact 

 suggests the possibility that the Golgi apparatus may be of the usual 

 form, even in those organisms in which the band, or ring, type has 

 been observed. Identification of osmiophilic substances answering the 

 known criteria for the Golgi apparatus has been extended to include 

 representatives of the four classes of Protozoa: Mastigophora, Sarcodina, 

 Sporozoa, and Ciliata. This substantiates the idea that the Golgi apparatus 

 is a cytoplasmic inclusion of all living cells. 



Conclusion 



In spite of the multiplicity of claims, counter claims, theories, and 

 suggestions, a few generalizations seem to be established well enough to 

 indicate at least some of the fundamental processes associated with ac- 

 tivity of the contractile vacuole. It is not intended that these shall be 

 accepted as proved beyond question, but rather that the evidence points 

 in their direction more consistently than in any other. Further investiga- 

 tion may necessitate a complete revision of opinion concerning these 

 processes, but in the light of the information available at the present 

 time the following conclusions seem to be justified. 



1. Contractile vacuoles originate as a result of the activity of certain 

 cytoplasmic inclusions, which may be aggregated in the immediate vicin- 

 ity of the vacuole in some species, or distributed more or less generally 

 throughout the cytoplasm in others. Temporary contractile vacuoles are 

 formed by the fusion or coalescence of small accessory vacuoles, which 

 in turn originate by the fusion of still smaller accessory vacuoles, the 

 last and smallest vacuoles being formed in or associated with the cyto- 

 plasmic inclusions mentioned above. More or less permanent contractile 

 vacuoles (e.g., those of Paramecium) receive fluid as small droplets, or 

 accessory vacuoles which fuse with some portion of the filling canals; 

 these droplets originate in or on cytoplasmic inclusions in the same man- 

 ner as those mentioned above. 



2. On the basis of known physicochemical laws and processes, it is 

 necessary to postulate the existence of a physiological membrane sur- 

 rounding the contractile vacuole. In some organisms, particularly those 



