496 LORANDE LOSS WOODRUFF AND RH. ERDMANN 



line of Paramaeciuni. Jennings in his extensive studies on this 

 organism has been able to discover only variations about the mean 

 in pure lines without conjugation. These variations about the 

 mean, we believe, are probably brought about, in p9,rt at least, 

 by endomixis because, although there is no opportunity in this 

 process for an introduction of foreign nuclear material, never- 

 theless there is an opportunity for its rearrangement. But Jen- 

 nings admits that ' ' There remains the possibility that heritable 

 variations of a totally different (lesser) order of magnitude may 

 arise during vegetative reproduction" ('13, p. 355). There is 

 no evidence from the race of Paramaeciuni which is the basis 

 of our studies that variations in morphological features or in 

 the division rate have occurred during its long cultivation which 

 have been inherited — the animals of the 4500th generation being 

 apparently in all ways similar to those of the early generations 

 — but we wish to point out that, a priori, endomixis affords a 

 field for the origin of such variations. It is conceivable that 

 ■'heritable' variations may result from some rare recombinations 

 in endomixis. Biometrical studies of animals in isolated lines 

 subsequent to endomixis are highly desirable. 



In higher organisms fertilization has a dynamic as well as a 

 hereditary role, and that these may be separated is amply at- 

 tested by so-called artificial parthenogenesis. In the conjuga- 

 tion of Paramaecium, Calkins, among recent investigators, has 

 put emphasis on the dynamic aspect, though admitting the 

 probability that conjugation is a source of variation; while Jen- 

 nings definitely states that ''There is no evidence that conjuga- 

 tion in the infusoria increases the reproductive power or reju- 

 venates the organism physiologically in any way" and puts all 

 the emphasis on the side of variation and heredity. 



Endomixis does initiate a new rhythm in the life history of 

 Paramaecium, i.e., a period of increased metabolic activity and 

 therefore of reproductive activity, and since its fundamental 

 morphological features are almost identical with those prelimi- 

 nary to the formation of the stationary and migratory micro- 

 nuclei in conjugation, it lends strong support to the view that 

 the dynamic aspect of conjugation is not absent. 



