Reproduction and Life-Cycles 85 



account has not been confirmed. Diller's observations on P. aurelia have 

 been followed by descriptions of autogamy in P. bursaria (5o) and P. 

 trichium (72). Cases of autogamy in which ciliates form a conjugant pair 

 but fail to exchange pronuclei have been referred to as cytogamy in P. 

 caudatum (243). In addition, certain genetic data (Chapter IX) agree with 

 the cytological evidence for autogamy in Paramecium. Up to a certain 

 point, nuclear behavior in autogamy parallels that in conjugation. Mat- 

 uration divisions are normal and pronuclei are formed. Instead of recip- 

 rocal transfer, however, fusion of two pronuclei occurs within the same 

 ciliate. It is uncertain whether autogamy is a normal process in its own 

 right or merely abortive conjugation. Chen (55) has found that, in con- 

 jugating trios of P. bursaria, a small area of cytoplasmic contact will 

 initiate autogamy in the odd member which is left out of the normal 

 pairing. 



Conjugation 



The onset of conjugation in mass cultures of certain ciliates is 

 indicated by a tendency for the organisms to adhere on contact, some- 

 times forming clumps containing many individuals. The nature of this 

 mating reaction is uncertain, although such a process suggests that the 

 ciliates develop sticky surfaces. This initial reaction in Paramecium 

 bursaria (126) seems to involve chance contact which leads to clumping. 

 In general, such a preliminary reaction seems to be independent of later 

 pairing and may be insignificant, or may not occur at all, in certain clones 

 of P. bursaria and in various other ciliates. The stalked conjugant of 

 Vorticella microstoma seems to exert some sort of attraction for motile 

 microconjugants passing within a distance of a millimeter (88). 



Clumping in P. bursaria is followed, after a half hour or so, by gradual 

 breaking up of the aggregates. At the end of several hours, only pairs and 

 single ciliates remain as a rule. Groups of three or four persist occasion- 

 ally, but only two members of each group are properly paired for con- 

 jugation (55). Pairing seems to depend upon favorable conditions and 

 may be influenced by temperature and intensity of light. 



The positions assumed by the paired conjugants (Fig. 2. 19) and the 

 extent of cytoplasmic fusion vary with the species. Contact commonly in- 

 volves the peristomial areas of the two conjugants. However, fusion at 

 the posterior ends occurs in Ancistrocoma myae (154), and fusion of oral 

 to aboral surface in Kidderia mytili (141). Among the Peritrichida, the 

 microconjugant becomes attached near the aboral end of the body in 

 Opisthonecta (211) and Vorticella, but near the oral end in Scyphidia 

 (233). In certain Apostomina, conjugants in lateral contact undergo re- 

 peated fission to produce chains and conjugation then proceeds between 

 corresponding members of the chains (47). The extent of fusion in con- 

 jugation apparently is influenced by the nature of the body wall. In 



