SEX IN PROTOZOA 229 



niicroiuiclcar division hccnnic the new niicronucleus. Most of these 

 accounts are not siifiicicntly detailed to determine just what kind of 

 reorganization takes place. They could be "endomixis," hemixis, au- 

 togamy, or parthenogenesis. However, Corliss (1952a, b) has re- 

 cently described in detail an autogamous nuclear reorganization in 

 the cysts of Tetrahyviena rostrata. Apparently this is the first clear 

 account of autogamy in a ciliate cyst. Doubtless other cases of autog- 

 amy will be found. 



Order Peritricha 



Since the time of Ehrenberg (1838) it has been observed that the 

 members of the Peritricha (especially the Vorticellidae) conjugate in 

 a manner different from the typical pattern. One or more preliminary 

 cell divisions produce larger and smaller conjugants. Figure AG (17) 

 shows a microconjugant and a macroconjugant being formed by a 

 single division of a '"neutral" individual of Vorticella microstoma, as 

 described by Finley (1943). The microconjugant becomes detached, 

 becomes motile, and swims about until it finds a macroconjugant with 

 which it unites. Variations in the formation of microconjugants con- 

 sist of one, two, or three divisions producing two, four, or eight 

 microconjugants from the first smaller animal derived from a "neu- 

 tral" individual. Finley and Nicholas (1950) found that four micro- 

 conjugants were produced from the smaller product of the first "sex- 

 segregating" division of Rhabdostyla vernalis. According to Finley 

 (1943) the macroconjugant is attractive to the microconjugant for 

 about 2 hours. Presumably a micro- and macroconjugant from the 

 same parent could conjugate together. Several microconjugants may 

 attach to one macroconjugant (Fig. AG, 18). 



The nuclear details are shown in Fig. AG (1 to 16) as illustrated 

 by Maupas (1889). Here it will be seen that there are three prelimi- 

 nary micronuclear divisions in the microconjugant but only two in 

 the macroconjugant (1 to 5). After these preliminary divisions one 

 nucleus in each conjugant survives and divides to produce pronuclei 

 (6 to 8), but only one of those in the macroconjugant fuses with one 

 from the microconjugant to form a syncaryon (9), By three divi- 

 sions, the fusion nucleus gives rise to eight nuclei (10 to 13) of which 

 sevTn enlarge as anlagen while one becomes the micronucleus (14). 

 Accompanied by micronuclear divisions, the anlagen are segregated 



