GEOTROPISM IN PARAMOECIUM 189 



dently very slight and its effect is easily annulled by the action 

 of other agents." 



SUMMARY OF RESULTS 



t. Paramoecia which have ingested a certain amount of 

 finely divided iron show temporarily an increased upward orient- 

 ing tendency which persists as long as the particles remain in the 

 posterior end, and tends to disappear as they become scattered 

 more evenly through the endoplasm. 



2 . The passive sinking of the posterior end is able to orientate 

 the animal into a position of gravity equilibrium with anterior 

 end up, only when it is moving in a narrow spiral or nearly 

 straight path. Overloaded individuals which are impeded in 

 their upward movements by the load begin to move in a broad 

 spiral and so change their course eventually to a downward 

 direction in the path of least resistance. 



3. A magnet placed at one side of a jar containing Paramoecia 

 which have ingested iron causes an upward streaming in the 

 stronger part of the field. Those heavily loaded animals which 

 move upward in this stream after dispersing above into the weaker 

 part of the magnetic field tend to sink again and cause a return 

 circulation to the bottom. 



4. The magnet is effective in producing this circulation by 

 diminishing the effect of gravity on animals containing iron. 

 It also exerts a passive pull upon them and they gradually 

 swing into their finally oriented position in a vertical path under 

 the combined influence of the magnet and gravity. The oriented 

 path is consequently a curve. 



REFERENCES 



Davenport, C. B. Experimental Morphology, vol. 1, N. Y. 



Harper, E. H. The Geotropism of Paramoecium. Jour, of Morph., vol. 22, 



1911. no. 4, pp. 993-1000. 

 Jennings, H. S. Behavior of the Lower Organisms. New York. 



1906. 

 Jensen, P. Ueber den Geotropismus Niederer Organismen. Arch. /. d. ges, 



1893. Physiol, LIII, 428-80. 

 Lyon, E. P. On the Theory of Geotropism in Paramoecium. Amer. Jour. Physiol., 



1904. XIV., 421-32. 

 Moore, A. Some Facts Concerning the Geotropic Gatherings of Paramoecium. 



1903. Amer. Jour. Physiol. IX, 238-244. 



