272 



J. F. McClendon 



one another. It has been shown above that the pressure in the 

 centrifuge reduces the size and probably increases the density 

 of the Paramoecia. This might cause them to go to the bottom 

 even though they preserved a negatively geotropic orientation. 

 I found the time elapsing before the return of the negatively geo- 

 tropic reaction to roughly correspond to the time required for the 

 return of the nuclei to their normal position. This might indicate 

 that the nuclei in normal position acted as statoliths. The fact 

 that the Paramoecia are constantly revolving on their long axes 

 does not prevent the application of the statolith theory, because 

 Paramoecia moving horizontally do not react to gravity (Jennings 

 '04) ; it is only w^hen they start to sw^im dovv^nward that they react. 

 I kept Paramoecia in the centrifuge for various periods of time 

 up to one v^eek to test whether distance from the nucleus would 

 effect the structure of the ectoplasm, and obtained only negative 

 results. Probably the circulation of the endoplasm is sufficient 

 to equalize the distribution of substances diffusing out of the 

 nucleus. In case gum solution was used control experiments 

 of Paramoecia in gum but not centrifuged were made. The gum 

 was eaten and gave the Paramoecia a slightly swollen, vacuolated 

 appearance. Some of the experiments are tabulated below: 



In those marked with * no gum was used. 



A marked effect on the rate of division was noticed in individ- 

 uals taken from the centrifuge. It has been shown by Calkins 



