THE INFLUENCE OF GENERAL ENVIRONMENTAL 



CONDITIONS ON THE PERIODICITY OF ENDO- 



MIXIS IN PARAMECIUM AURELIA. 



LORANDE LOSS WOODRUFF, 

 OSBORN ZOOLOGICAL LABORATORY, YALE UNIVERSITY. 



(Twelve figures.) 



It is clear from the evidence submitted in previous papers 

 that there are normal, minor, periodic fluctuations (rhythms) in 

 the rate of reproduction of Paramecium, 1 and that at the low 

 point in the division rate between two rhythms there normally 

 occurs an intracellular reorganization process (endomixis). 2 The 

 data previously presented also show that in Paramecium aurelia 

 endomixis occurs, generally speaking, at intervals of about four 

 weeks or about fifty generations, and that the synchronism of the 

 process in different lines of the same race under identical condi- 

 tions is remarkably exact. 3 But, as was stated incidentally, on 

 the basis of our experience in working out the cytological phe- 

 nomena of endomixis: "It is possible to retard or hasten the 

 occurrence of the process by the character of the culture medium. 

 For example, it may occur a few days earlier in animals not 

 supplied daily with fresh culture fluid than in the regular lines." 4 

 Such being the case it is important to determine the influence 

 of environmental conditions on the duration of the rhythms 

 and the occurrence of endomixis. 



The present paper comprises chiefly a study of the effects 

 of what may be termed general changes in the culture conditions, 



1 Woodruff and Baitsell, "Rhythms in the Reproductive Activity of Infusoria," 

 Journ. Exper. Zool., XL, 4, 1911. 



2 Woodruff and Erdmann, A Normal Periodic Reorganization Process without 

 Cell Fusion in Paramecium," Journ. Exper. Zool., XVII., 1914; Erdmann and 

 Woodruff , The Periodic Reorganization Process in Paramecium caudatum," Journ _ 

 Exper. Zool., XX., 1916; Woodruff, "Rhythms and Endomixis in Various Races of 

 Paramecium aurelia," BIOL. BULL., XXXIII. , 1917. 



3 Cf. Woodruff and Erdmann, 1914, Tables i, 2, 3. 



4 Woodruff and Erdmann, 1914, p. 485. 



437 



