The Chattons2 and Zweibaum3 have maintained that conjugation is entirely determined by environmental conditions.Others (Sonneborn and Cohen4 and Sonneborn and Lynch5) have shown that genetic factors are also involved.The present results show the overwhelming importance of genetic factors in some stocks.(3) Calkins and Gregory6 long ago attempted to show that the de- scendants of the four products of the first two fissions after conjugation in P. caudatum (where four instead of two macronuclei are formed in each exconjugant) were genetically diverse.The present work confirms this principle in a striking way.It may perhaps be said that with the present work the genetics of Para- mecium enters the quantitative and predictable stage, with tools and methods of analysis which should lead rapidly into a systematic, coherent body of knowledge in close touch with the rest of genetic sdence.
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Rôbbins et al. (1937) studied this question.