80 KHODA ERDMANN AND LORANDE L. WOODRUFF 



nature had only been suspected ('14, III, p. 430), and stated 

 ('14, III, p. 481) "Therefore, it is evident not only that the 

 reorganization process is coincident with the low points between 

 two rhythms, but also that there is a causal relation between the 

 reorganization process and the rhythms." 



We have now established this same conclusion for Paramaecium 

 caudatum. In our races of this species, however, the endomictic 

 periods appear at intervals of about 50 to 60 days, or from 80 

 to 100 generations, instead of from 25 to 30 days, or 40 to 50 

 generations as in Paramaecium aurelia. But they are funda- 

 mentally the same morphologically and physiologically in both 

 species. 



Text fig. 6 Graph of tlie rate of division of Culture Z, Line I, averaged for 

 five-day periods. The periods during which the reorganization occurred are 

 indicated by a X. Cf. page 71, table 3; and also Woodruff and Erdmann, '14, 

 III, text figures 16 and 17. 



Now a critical examination, in the light of our present knowl- 

 edge of endomixis, of the division rate of Calkins' pedigreed 

 culture of Paramaecium caudatum, the study of which led him 

 to his well known conception of protoplasmic old age in Protozoa, 

 shows clearly that his periods of degeneration can be perfectly 

 interpreted as endomixis (text fig. 7, copied from Calkins). 

 Woodruff in an early paper ('09, p. 300) wi'ote: 



1 have previously interpreted as rhythms the tri-nionthly depres- 

 sions in vitality, whicli Calkins and earlier workers on Paramaecium 

 have noted, and the results olitained from mj^ culture of Paramaecium 

 seem to indicate that the semi-annual cycles of Calkins are also actually 

 rhythms, recovery from which was not autonomous under the con- 

 ditions of a constant environment. The general occurrence of rhythms 

 in the life history of infusoria is estal^lished, I lielieve, l)nt to what they 

 are due is still awaitinff discoverv. 



