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H. S. JENNINGS 
question, how often can reconjugation occur in a single line of 
succeeding generations from a single individual? 
On this question certain interesting data are given by my 
experiments with kh. This, as we have seen, is a single ex-conju- 
gant, one of a pair of k that were conjugating November 9, 1908. 
From this, two diverse lines were cultivated with frequent recon- 
jugation, with history as follows: 
First conjugation November 9: a single member of the pair 
multiplied till April 17 (with in the meantime many epidemics of 
conjugation among its progeny). Conjugation April 17: a single 
exconjugant {ko) isolated and allowed to multiply till May 19, 
when conjugation occurred among its progeny. A single member 
of a pair {koc) was again isolated after conjugation, and allowed 
to multiply. In the fourth generation, after but 16 individuals had 
been produced, conjugation again occurred among its progeny, 
giving after separation the individuals koca. This generation 
was unfortunately destroyed. The pedigree of koca may then be 
represented as in fig. 2. 
kb ko koc koca 
Nov. 9 April 17 May 19 May 24 
Fig. 2 Diagram showing the conjugations in the pedigree of koca. The fissions 
intervening between the conjugations are omitted. Each pair derived from a 
single member of the preceding pair. 
We have thus four conjugations in series — the two members 
of any given pair being progeny of a single member of the preceding 
pair. Whether this inbreeding for four generations affects the 
stock in any way we shall discuss elsewhere. 
Tn another case inbreeding has continued for five conjugations 
in series. From the conjugating pair of November 9, a single 
individual {kh) gives a numerous progeny, with frequent epidemics 
of conjugation among themselves. From one of these on March 
9, twenty-five pairs were selected and placed together, producing 
numerous progeny (all of whose parents had thus certainly con- 
