354 EDWIN G. CONKLIN 



after centrifuging. External surface tension can not therefore 

 be the cause of the normal positions of cell parts or of their 

 return to these positions after centrifuging. Probably internal 

 surface tension between the different constituents of a cell may 

 play a more important part in localization of these constituents, 

 but even this would not account for the persistence of polarity 

 in centrifuged eggs unless there is some portion of the cell which 

 remains unmoved during centrifuging. 



Since surface tension increases with decreasing temperature 

 and vice versa an attempt was made to detennine whether the 

 return to their original positions of cell substances or parts which 

 have been displaced by centrifuging is hastened by lowering the 

 temperature. Eggs in various stages of development were cen- 

 trifuged for 10 minutes and then placed for varying lengths of 

 time on ice where the temperature was about 2°C., while one 

 control was kept at room temperature (about 20°C.) ; in another 

 experiment the temperature was raised to about 35°C. That 

 the surface tension of these eggs is increased by lower tempera- 

 tures is indicated by the fact that eggs are more nearly spheri- 

 cal at lower temperatures than at higher ones, but the results 

 showed conclusively that the return of cell parts to their normal 

 positions took place more rapidly at about 20° than at 2°, thus 

 indicating that this return is not due to internal or external sur- 

 face tension. It is true that viscosity increases at lower tem- 

 peratures as well as surface tension, nevertheless it does not pre- 

 vent the eggs from assuming a spherical form; for these reasons, 

 as well as for those mentioned above, it is evident that neither 

 external nor internal surface tension is the principal cause of the 

 normal location of cell parts nor of their return when once they 

 have been displaced. However it is not denied that internal 

 surface tension may be one of the contributory factors in the 

 return of displaced substances, such as yolk, to their normal 

 positions. 



3. Spongioplasmic fraviework as the cause of polarity. There 

 remains the explanation which has been maintained throughout 

 this paper, namely, that the orientation and localization of cell 



