PARAMOECIUM POSSESSING EXTRA VACUOLES 325 



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that controls the production of the vacuoles since their produc- 

 tion seems to be controlled by so many conditions Whether 

 these conditions act on the cytoplasm directly or on the cyto- 

 plasm through the nucleus there is no possibility of determining 

 with the knowledge available at present. 



IX. SUMMARY 



1. This race which is a variety of Paramoecium caudatum is 

 considered possibly to have arisen under experimental conditions 

 when certain animals were subjected to high temperatures. 



2. The animals of this race range in length from 167 m to 307 m 

 and are unusually strong and resistant. 



3. A slightly denser portion extends across the middle of 

 some of the individuals as a band. 



4. The extra vacuoles are generally located in the posterior 

 end of the cell. 



5. The number of vacuoles possessed by individuals of this 

 race varies from two to seven. 



6. The number of vacuoles may increase during the life time 

 of the individual. 



7. Various conditions affect the number of vacuoles present 

 in the individual, such as the rate of division and the age of the 

 cultm'e medium. 



8. Though extra vacuoles may not appear for several genera- 

 tions for the above reasons, the potentiality for this organ has 

 not been lost. 



9. The division rate ranges between one and five times in 

 twenty-four hours. 



10. Besides being influenced by the rate of division the 

 vacuole number may apparently be increased in the individual 

 by the presence of katabolic products in the environment. 



11. The resistance of this race to .heat, cold, distilled water, 

 etc., is very high. 



12. The rate of pulsation of the vacuoles is slightly slower 

 than is that of the vacuoles in the common race but the new 

 animals are in general superior to the common race in their 

 powers of excretion. 



THE JOUHNAL OF EXPERIMENTAL ZOOLOGY, VOL. 23, NO. 2 



