THE CONTRACTILE VACUOLE 431 



cell, but beyond this the interpretation is subject to criticism. As stated 

 by Calkins (1926), these supposed functions are not necessarily exclu- 

 sive, and the possibility still exists that other functions, as well as 

 these, are performed by the contractile vacuoles. 



Contractile Vacuoles and the Golgi Apparatus 



Few publications within recent years on the general subject of con- 

 tractile vacuoles have aroused as much interest or stimulated as much 

 constructive research as that of Nassonov (1924), in which he sug- 

 gests that the vacuole in Protozoa is homologous with the Golgi ap- 

 paratus in metazoan cells. Neglecting for the moment the ultimate status 

 of this proposed homology, one must admit that this article is responsi- 

 ble, either directly or indirectly, for valuable work which otherwise 

 might have been delayed indefinitely. 



Before attempting a discussion of the literature bearing on this pro- 

 posed homology, a few words concerning the general nature of the 

 Golgi apparatus may be of benefit. Its discovery in 1899 is attributed 

 to the man whose name it bears. For approximately twenty-five years 

 after the first description of such a structure its actual existence was 

 doubted by many competent cytologists. Demonstration of the Golgi 

 apparatus in most cells requires a somewhat rigorous treatment of the 

 tissue with various chemical agents, some of which may reasonably be 

 suspected of leaving in the cytoplasm chemical or physical changes of 

 such a nature as to be visible after the Golgi technique, when in reality no 

 such structures exist, pre-formed, in the cell. The problem is probably 

 complicated even further by the multiplicity of forms and shapes which 

 the Golgi apparatus is observed to assume in difi^erent cells. At present 

 there seems to be little doubt but that such structures exist, pre-formed, 

 in most cells. Many investigators go so far as to state that the Golgi 

 apparatus is one of two or three cytoplasmic constituents which are in- 

 variably present in all cells, both plant and animal. If this is true, then 

 it is probable that the role of the Golgi apparatus in the life history 

 of the cell is of very great importance. 



Demonstration of the Golgi apparatus, or Golgi bodies as the struc- 

 tures are frequently called, depends on the reduction of certain metallic 

 compounds to the free metals, the compounds most frequently used con- 

 taining either osmium or silver. The reduced metal results in blackening 



