SEX IN INFUSORIA 229 



in the endoplasmatic conjugation outgrowth of the macro- 

 conjugant. The only possible interpretation of such a pair is 

 the following one. The conjugants have reached the stage 

 of pronuclei. Both the pronuclei of the microconjugant have 

 migrated into the larger partner, while the corresponding 

 process in the latter was retarded so that the ' male ' pronucleus 

 of the macroconjugant has not yet succeeded in penetrating 

 into the partner. And we must say that, in the pair under 

 discussion, a further migration of the male pronucleus (Mij) 

 into the smaller partner would become absurd, as the corre- 

 sponding female pronucleus of the microconjugant (Mig) has 

 penetrated into the larger individual. Let us imagine that the 

 separation of such a pair is accomplished, and we should then 

 have before us a micro-exconjugant provided with only one 

 nucleus, the old macronucleus (as in the above-mentioned 

 abnormal exconjugant), and a macro-exconjugant with a 

 double set of nuclei. A strong confirmation of such an inter- 

 pretation is supplied by a macro-exconjugant in the stage of 

 reconstruction of the nuclear apparatus. In this specimen 

 there are two micronuclei and two macronuclei instead of one 

 micro- and one macronucleus. There, as I believe, the pro- 

 nuclei of the microconjugant penetrated into its partner (as 

 in the case mentioned above) and copulated with the corre- 

 sponding pronuclei — thus producing a pair of syncarya. The 

 latter then divided, giving rise to a double set of micro- and 

 macronuclei. The micro-exconjugant with an old macro- 

 nucleus and a small micronucleus (see above) is to be thought 

 of as a specimen whose ' male ' pronucleus has migrated into 

 the larger partner, while the corresponding migration of the 

 macroconjugant's ' male ' pronucleus did not take place ; and 

 the exconjugant represents, therefore, an individual with its 

 old macronucleus and a ' female ' pronucleus. 



These and some other abnormal cases give us grounds 

 enough for framing the following hypothesis. If analogous 

 anomalies become more common, a time may come when in 

 conjugating pairs only the ' male ' pronucleus of the micro- 

 conjugant will migrate, the reciprocal process being suspended. 



