2O SAKYO KANDA. 



already pointed out, Plait's method was not as accurate for 

 obtaining the density of the animals as Lyon's. We may there- 

 fore consider our results to be the more accurate. 



Then nine tubes about 12.5 cm. long and 0.4 cm. in diameter 

 were prepared. They were filled up to about 12 cm. with the 

 solutions of known density from 1.24 to 1.032 thoroughly 

 mixed with about two drops of the "wild culture" containing 

 dense spirostoma, free from sediment. Three drops of parafhne 

 oil were placed above the solution in each tube. 



The negative geotropism of spirostoma is not so marked as 

 usually supposed, and their movements under these conditions 

 were much slower than those of the paramecia in the preceding 

 experiments. About two hours after placing in the solutions 

 of the same density as their own a few rose up to about the 

 middle part of the tubes; a still larger proportion so rose in the 

 solutions of greater densities than their own, but in the solution 

 of 1.024 all were on the bottom, while in that of 1.025 a few rose 

 from the bottom of the tube to the height of 2.5 cm. This 

 suggests that the buoyancy in the solutions of greater densities 

 than their own helped the animals to rise. But about 13 hours 

 later, nearly all the animals in the solutions rose up to near the 

 top. Two weeks later some spirostoma were living in all the 

 tubes except one of 1.027 which was broken 4 days after treat- 

 ment. At that time the writer had to leave Woods Hole. 

 Meanwhile the number of the animals considerably decreased, 

 but in some tubes a few individuals divided. 



V. THE STATOCYST THEORY AND ITS CRITICISM. 



A fourth theory of geotropism proposed by Lyon is based on 

 the assumption that the Paramecium contains protoplasmic 

 materials of different specific gravity. "For internal stimulation 

 the relation of the parts of the cell to each other must be changed 

 in some way by grvaity. Stresses or pulls which occur when 

 the organism is in one position with respect to the vertical, 

 must be changed in another position" (17, p. 429). This is 

 called the "statocyst theory" of geotropism in the Paramecium. 

 It is worth while to mention, with reference to the general theory 

 of geotropism in animals, that Loeb in 1897 (15, pp. 446-449) 

 had already suggested a similar theory. 



