228 SEX IN MICROORGANISMS 



destroyed or changed to macronuclei; by the second method, micro- 

 nuclei grew into macronuclei. Amicronucleate animals were said to 

 be capable of "endomixis" (presumably hemixis or macronuclear re- 

 generation) with a repetition every 8 to 10 days. The macronuclei 

 (normally two) broke up and new macronuclei developed from 

 some of the fragments. Even amicronucleate animals were said to 

 "conjugate," the "conjugants" being of different sizes. The joined 

 animals fused into one, the macronuclei became resolved into ribbons, 

 then fragmented, and new macronuclei regenerated from fragments 

 the size of micronuclei. This process cannot properly be called con- 

 jugation in the absence of micronuclei. When amicronucleate animals 

 conjugated with normals, there was also complete fusion of the asso- 

 ciates, and presumably autogamy or parthenogenesis took place. 



Among the Peritricha, "endomixis" was described for a species 

 of Trichodina from tadpoles by Diller (1928). Later (1936) he 

 thought that exconjugant and hemictic stages might have been lumped 

 together as "endomixis," while Padnos and NigreUi (1942), after a 

 study of conjugation in Trichodina spheroidesi, thought that Diller's 

 "endomixis" could be reorganization in exconjugants. Faure-Fremiet 

 (1930) recorded nuclear changes under the term "endomixis" in 

 TjOotbmnniimi alterna7is, and Seshachar (1946) reported hemixis in 

 Epistylis plicatilis and E. anastatica. Willis (1948) recorded an appar- 

 ent endomixis in Lagenophrys tatter salli. 



Nuclear reorganization seems to occur more commonly in cysts 

 than during the active state. In my experience, it is common for the 

 macronucleus to undergo fragmentation in cihates after encystment. 

 Some of the ciliates which have been reported as undergoing nuclear 

 reorganization in the cyst stage are Uroleptiis mobilis (Calkins, 

 1919); Spathidiinn spathula (Moore, 1924); Eiiplotes longipes (Klee, 

 1926); Chilodonella uncinatus (Ivanic, 1928, 1933a, 1935b); Vorti- 

 cella nelnilifera (Ivanic, 1929); Urostyla graiidis (Tittler, 1935); and 

 Paraclevelafidia simplex (Kidder, 1938). In the last-named species, 

 the reorganization was of an unusual type. The micronucleus divided 

 into two. The macronucleus underwent a partial breakdown with 

 about half of its chromatin being eliminated through the reservoir of 

 the contractile vacuole. The remaining half rounded up and joined 

 with one micronucleus to form a new macronucleus. This passed 

 through a "ball-of-yarn" stage like that in the exconjugants of Nycto- 

 therus cordijorviis and some other ciliates. The other product of 



