Protozoan Studies 271 



Paramoecium and lost, or whether the Paramoecium is the result 

 of a division in the centrifuge in which one daughter was pre- 

 vented from receiving nuclear material by the centrifugal force, it 

 is impossible to say. I have found what appeared to be division 

 stages in specimens just taken from the centrifuge. However, 

 if the centrifugal force had been great the process of division in 

 these specimens was usually not continued, but the elongate and 

 sometimes partially constricted animal would swim about for 

 days without undergoing much change before death. Fig. 5 is of 

 a specimen centrifuged 24 hours, nV = 742 X 10^. The poste- 

 rior end was turned outward, and both nuclei have crowded into 

 that end. All the Paramoecia subjected to this experiment were 

 very small at its close, probably due to loss of water under the 

 increased pressure. 



Judging from many individuals, the time that the macronucleus 

 remained displaced after removal from the centrifuge was about 

 the same as the time it had probably remained displaced in the 

 centrifuge. Many exceptions to this rule, and the fact that some 

 individuals changed their orientation while in the centrifuge, 

 makes an exact statement impossible. 



E. P. Lyon ('05) showed that Paramoecia centrifuged for some 

 time are not negatively geotropic. If the geotropic reaction be due 

 to the pressure in one direction of substances in the Paramoecium 

 of specific gravity different from the surrounding protoplasm, 

 (statolith theory) an abnormal displacement of such substances 

 might upset the mechanism of geotropism. I found in con- 

 firmation of Lyon's results that Paramoecia recently taken from 

 the centrifuge are not negatively geotropic but apparently swim 

 as often in one direction as in another and gradually reach the 

 bottom by their own weight. Great care must be used in this 

 experiment to rid the Paramoecia of gum if they have been put 

 in it, as Ostwald ('06) has shown that altered viscosity of the 

 medium may change the sign of the reaction. Jensen ('93) has 

 shown that Paramoecia are positively geotropic on hot days, and 

 the friction of the air may raise the temperature of fluids in the 

 centrifuge. The effects of a rise of temperature and increase in 

 viscosity due to a Httle gum in the medium would tend to neutralize 



