REGENERATION IN PARAMECIl'M CAUDATUM. 



165 



end is removed than there is when the posterior end is cut off. 

 This table does not show the tre- 

 mendous differences in the behav- 

 ior w T hich result from the condition 

 of individual cells at the time of 

 the operation. There is a definite 

 correlation between the behavior of 

 fragments and the periods of depres- 

 sion to which cultures are subject. 

 At such times a race which normally 

 shows great power of regeneration 

 fails both to regenerate and to divide. 

 The power to regenerate is not so 

 much a characteristic of a race as it is 

 an indication of the vitality of the 

 individual cell. Paramecium taken 

 from a pure line will regenerate in 

 ninety cases out of a hundred if the 

 cytoplasm is in a viscid state and 

 the animals are well fed. When the 

 cells are starved or in a period of 

 depression from other causes, the rate 

 of division is slow and the power of 

 regeneration is greatly reduced or al- 

 together lost. 



FIG. 14. Diagram giving the 

 history of a fragment cut close 

 to the nucleus. 



H. Can the Size of a Race be Reduced by Removal of Part of the 



Cytoplasm? 



In his extensive and careful investigations on Paramecium 

 Jennings ('10) has shown that race size is inherited and that a 

 new race of a different size does not arise within a pure line. 

 Popoff ('09) claims that it is possible through experimental means 

 to change the size of the race and to maintain the altered cell size 

 for an indefinite period. The forms upon which Popoff made his 

 observations were Frontonia leucas and Stentor ccerideus. 



In order to determine whether or not a loss of cytoplasm alone 

 would reduce the size of a race permanently I undertook a long 



