94 



SAKYO KANDA. 



seems to be about 56. The inference may be made that positive 

 geotropism in Physa is an active process, and that negative geo- 

 tropism, on the other hand, is due largely, though not entirely, 

 to "passive orientation." 



The so called mechanical theory of geotropism, however, can 

 not be applied even in the case of negative geotropism. This is 

 obvious when one remembers that Physa becomes negative to 

 gravity when "its lung is empty," even though its specific 

 gravity is less than that of water; and positive when its lung is 

 full of air, even though its specific gravity is greater than that of 

 water. The essential factors, therefore, which determine the 

 geotropic orientation, either positive or negative, of Physa seem 

 to be internal, that is, physiological ones (cf. 3, 4, 5, 7, 8 and 

 9 in the bibliography). 



TABLE VI. 



GEOTROPISM OF Physa AT THE DIFFERENT ANGLES OF INCLINATION OF A SMOOTH 

 GLASS PLATE IN THE AIR IN TOTAL DARKNESS. 



At beginning of experiments, each head placed upward. Table shows results 

 after one minute. 



From the above results the writer thinks that both Walter 

 and Dawson overlooked the fact that Physa is naturally positively 

 geotropic. 



(b) Experiments with a Ground-Glass Plate. Contact stimuli, 

 as stated, affect the behavior of animals. Supposedly it might 

 affect the geotropism of Physa. The same methods were used 

 here as in the above. The results given in Table VII. show a 

 fair agreement with the above supposition. 



