SAKYO KANDA. 



downward, even though the "shock" lasts only a moment. 

 Moreover, as Sosnowski (23, p. 134) and Moore (19, pp. 239-241) 

 have shown, the animals are negatively geotropic at 2 C., while 

 they are positively geotropic at 30 C. As we have already 

 pointed out, certain spiders whose posterior region is much 

 heavier than the anterior, nevertheless orient themselves, when 

 at rest with their head down. Therefore we conclude that 

 without consideration of the internal factors, we have difficulty 

 in explaining the facts, even though we do not absolutely reject 

 the external factors. 



A possible method which the writer intends to try later would 

 consist in the following: Immediately after centrifuging a capil- 

 lary tube containing paramecia, and in which the latter cannot 

 turn around, we may stain them with some dyes and determine 

 the effects of the centrifugal force upon the protoplasmic mate- 

 rials of the organisms. The application of this or similar methods 

 is of the utmost importance for the problem of geotropism not 

 only in paramecia but in animals in general. 



VII. SUMMARY. 



1. Paramecium caudatum and Spirostomum teres assume a 

 position wdth their anterior ends directed away from the axis 

 of the centrifuge. Their anterior ends, therefore, must be 

 heavier than their posterior ends. If so, the negatively geo- 

 tropic orientation is an active process and the mechanical theory 

 cannot be held. 



2. It is not conceivable that the animal could be sensitive to 

 slight differences in pressure such as W 7 e have computed must 

 exist between the two sides or the two ends of its body. There- 

 fore the pressure theory is not tenable. 



3. Paramecium and Spirostomum in the gum-arabic solutions of 

 greater, equal, and less specific gravity than their own are still 

 negatively geotropic. Therefore the resistance or weight theory 

 is not correct. 



4. The specific gravity of living Paramecium caudatum is 

 about 1.037 or T - 37 =*= 0.003. 



5. The specific gravity of living Spirostomum teres is about 

 1.025 or 1-025 0.003. 



6. The statocyst theory of geotropism is the most tenable. 



