IO6 S. O. MAST AND YASUSHI IBARA. 



perature is not, although she found encysted specimens during the 

 winter months. Miss Hogue contends that the accumulation of 

 waste products is the primary cause of encystment. She says, 

 referring to Anieba liina.v (1914) : "The condition under which 

 they encyst seems to point to a weakened vitality. It seems as 

 though the digestive fluid has not been formed in sufficient quan- 

 tity, owing to the rapid division. So it is not the lack of food, but 

 rather the loss of power of assimilation." And (1917, p. 5/1) : 

 ' When the accumulation of waste product is very great, and the 

 Amoeba: have multiplied so fast that there is no further place for 

 them to go, they encyst. I have frequently observed a culture dish 

 containing thousands of Amoeba:, with plenty of food, soon become 

 covered with cysts, the Amoeba: having often encysted over night." 



It is generally held that encystment is a protective adaptation. 

 Thus Calkins says (1910, p. 40): 'This is a special adaptive 

 process by which the organisms are enabled to survive when the 

 environment is unsuitable." (P. 90) "There is a general agree- 

 ment that its object is to protect the individual during periods of 

 drought, cold, or periods of reproduction." (P. 192) "It occurs 

 when the animal is in danger of drying, or in some cases before 

 division, in others for the purpose of digesting a full meal." Min- 

 chin (1917) expresses similar views, as does also Jordan. Jordan 

 says (1918, p. 73) : "It serves to tide the species over a period of 

 dryness, famine, or unsuitable temperature, and to preserve alive 

 in a hostile environment a sufficient number of individuals until 

 such time as favorable conditions recur. The spore-stage is in 

 fact physiologically analogous to the periods of hibernation and 

 estivation among the higher forms of life. In this resting state 

 the living matter of the spore may remain dormant for years or 

 even for decades." 



It seems evident, then, that many investigators hold that encyst- 

 ment is induced by adverse changes in the environment, and that 

 it protects the organism against unfavorable conditions. The evi- 

 dence presented in favor of the first of these contentions is, how- 

 ever, not strong. A thorough experimental investigation of the 

 relation between the environment and encystment is, therefore, 

 highly desirable. 



In this paper we shall present the results obtained in experi- 



