2 SAKYO KANDA. 



and experimental reexamination the various theories of geo- 

 tropism in the protozoa, especially in Paramecium and Spiro- 

 stomitrn. The experimental work has been largely confined, 

 with variations, to the repetition of the work of Lyon and 

 Harper. 



As is well known, paramecia are extremely sensitive to chemi- 

 cals or food, to contact stimuli, to water currents, to mechanical 

 agitation, to changes of temperature, etc. For geotropic experi- 

 ments, therefore, the sources of those stimuli must be carefully 

 excluded. If this has been done and if paramecia washed in 

 pure distilled water are placed in a vertical clean glass tube, 

 they swim upward and gather at the top. In other words, 

 paramecia under proper conditions are negatively geotropic. 

 But Sosnowski (21, p. 131), Platt (20, p. 32), Jennings (9, p. 473; 

 10, p. 76), Lyon (17, p. 421), Harper (3, p. 995) and others 

 have found considerable variation in the behavior of individuals 

 in different cultures; some orient themselves downward and 

 swim in that direction, while others are apparently indifferent 

 to gravity. Nevertheless, in the majority of cases there is no 

 doubt that gravity is the real "directive force." We are thus 

 confronted by the established fact of negative geotropism in 

 paramecia, but different investigators offer varying explanations 

 for the phenomenon. 



II. THE MECHANICAL THEORY. 



From his study of the reactions of Euglena and Chlamydomonas 

 to gravity, Schwarz in 1884 reached the conclusion that the 

 negative geotropism of these animals is due to the direct influence 

 of gravity on the organisms, inciting movement in the opposite 

 direction (22). Aderhold in 1888 investigated Euglena (i, pp- 

 317-320) and Desmid (i, pp. 339-340), and came to the same 

 conclusion as Schwarz. 



Though he seems now to accept the "statolith theory" (25, 

 pp. 526-527), Verworn claimed at first that the effect of the 

 force of gravity exerted upon the protozoa is "purely physical" 

 (24, p. .121). According to him, "the protoplasmic mass of 

 greater specific gravity sinks toward the bottom . . . , while 

 that of less specific gravity rises toward the surface and stays 



