6 SAKYO KANDA. 



"the explanation here given" "seemed to him the most satis- 

 factory explanation of the fact that all are found to move with 

 the anterior end outward" (3, p. 998). This suggestion of 

 Harper is worth serious consideration as a criticism of Lyon's 

 experiments, and must not be overlooked; because we know 

 from Sosnowski (23, p. 133) and Moore (19, p. 243) that para- 

 mecia which have gathered at the top of a tube often become 

 positively geotropic by a "shock" or "mechanical agitation." 

 The present writer also found this to be true. But two series of 

 questions arise: (a) What makes the animals swim downward 

 after the mechanical shock or agitation? If the "pull of gravity ' 

 "is too weak to stimulate," it should not produce a positive 

 geotropism any more than a negative one, because the pull of 

 gravity always remains the same before and after the mechanical 

 shock. In Lyon's centrifugalization experiments, however, the 

 "substituted" centrifugal force continued to act until the ani- 

 mals were carried into the capillary tube where they could not 

 turn around. Centrifugalization and temporary mechanical 

 agitation have thus different effects. And (b), if the posterior 

 end of the animals is "heavier" than the anterior end, as Harper 

 claims, is it possible that the animals, when strongly centrifuged, 

 are really "able to react at the outset of centrifugalization," so 

 as to direct themselves with the "lighter" anterior end away from 

 the axis of the centrifuge? If we believe in a mechanical ex- 

 planation in this case, as Harper does in the normal case of the 

 "passive orientation," we should hardly expect that this would 

 be the case, because Lyon employed too strong a centrifugal 

 force and the mechanical effect is proportioned to the force 

 acting. It seems to us therefore that the question remains 

 unsettled, though Harper seems satisfied with the mechanical 

 theory. 



In his second series of experiments, Harper used a strong 

 electromagnet applied to the iron-ingested paramecia. From 

 the results, he concludes that "the passive sinking of the posterior 

 end is able to orient the animal into a position of gravity equilib- 

 rium with the anterior end up" (4, p. 189). As to the magnetic 

 effect, he thinks that it caused in the iron-ingested animals "an 

 upward streaming in the stronger part of the field. Those heavily 



