12 SAKYO KAXDA. 



which bring about orientation. But it is not the only condition 

 because, as we have already observed, the negative geotropism 

 of the normal paramecia may be altered by a mechanical agitation 

 to a positive geotropism. We must, therefore, hold with Moore 

 (19, pp. 243-244), Jennings (10, p. 99), and Lyon (17) that there 

 are some additional internal or physiological conditions of 

 orientation in such a case. 



Experiment d. In the experiments on iron-ingested para- 

 mecia the writer used an electromagnet not as strong as that 

 used by Harper, employing a binocular microscope placed 

 horizontally for the observations of the movements of the 

 animals, so adjusted that the experimental tube was readily 

 observed. The writer found in these experiments that many 

 animals swam upward, while others swam downward, and a 

 few others toward and away from the electromagnet, which was 

 applied at one side of the tube. According to Harper, the path 

 of paramecia so treated represents the resultant of the pulls of 

 gravity and of the electromagnet. The writer saw some behave 

 in this way, but he could hardly specify it as characteristic. 

 He was unable to detect any orientation with respect to the 

 magnetic force. Possibly the weak electromagnetic force in the 

 writer's case might be the cause of the difference between his 

 results and those of Harper. But even with such a weak force 

 it was observed in many cases that the pull of gravity was easily 

 obscured by the pull of the electromagnet. In a few cases it 

 was observed that the individual when passing in front of the 

 magnet was passively drawn backward toward it when the 

 electric current was connected and moved in a straight line away 

 from it when the current was disconnected. Such cases indicate 

 that the pull of gravity has no effect on the animal in comparison 

 with that of the electromagnet. 



2. Experiments on Spirostomiim teres. 



Experiment a. Spirostomiim teres is one of the largest of 

 unicellular organisms. The average length of those on which the 

 following experiments were made was about two tenths of a 

 millimeter. Spirostoma from a w r ild culture were centrifuged to 

 determine their position in a capillary tube in the same way 



