GEOTROPISM IN PARAMOECIUM 183 



intervals before rising. After the lapse of a half hour, more 

 or less, such a culture as this aggregates rather densely toward 

 the bottom, presumably as a result of ciliary fatigue. After 24 

 hours, or even less, they may all be found risen again and appar- 

 ently no worse for the treatment. 



When such a treated culture is placed in the field of the magnet, 

 as soon as the current is turned on there begins a strong upward 

 streaming past the pole and as a result a downward movement 

 also becomes manifest on the side away from the magnet. The 

 downward movement is wider and more diffuse than the upward. 

 The latter was a narrow stream up to a half inch in width. The 

 concentration of this upward streaming gives it a striking appear- 

 ance, while the downward movement is more scattered. Thus 

 the culture shows the decided appearance of being in a state of 

 circulation. Some of the Paramoecia in the upward stream 

 continue on up to the surface of the water, but more usually 

 they begin to disperse in all directions. They may move to a 

 short distance, meanwhile sinking, and return to the upward 

 stream, or they may go farther away before they finally sink. 

 A considerable aggregation is found in the outside lower corner, 

 i. e., away from the magnet. 



As to the explanation of the upward streaming, it is evident 

 that it involves explaining the upward orientation of the animals 

 and their ability to rise in the stronger part of the magnetic 

 field, while elsewhere they tend to sink. It is apparent that 

 the movement upward arises mainly from below the pole and 

 also from the side, and that it consists chiefly of upwardly oriented 

 animals which do not congregate at the pole, but rather move 

 more freely the nearer they are in its vicinity, and frequently 

 keep on going upward. They appear therefore to experience a 

 greater buoyancy in the magnetic field, so that we may assume 

 the effect of the magnet to be due to its diminishing the effect 

 of gravity upon the heavily loaded animals. Their upward 

 orientation is another matter and is explicable by gravity alone, 

 based on the observation that the posterior end is of higher 

 specific gravity than the anterior where the stronger cilia are 

 located. 



To better understand this we need to refer to Jennings' lucid 

 description of the action system of the animal. When Para- 

 moecium is unimpeded in its progress in any way it tends to 



