CONJUGATION IN PARAMCECIUM 93 



latter is alone concerned in the process of conjugation, the 

 meganucleus in the meantime breaking up and being absorbed 

 into the cytoplasm, to be replaced in the manner described later 

 on. We may confine our attention, therefore, to the behaviour 

 of the micronucleus. In each conjugant this divides mitotically 

 into two daughter nuclei (Fig. 41, B, mic.' and p.b.) each of which 

 again divides, so that there are now four micronuclei (Fig. 41, C). 

 Of these four three (p.l>-} go to the bad, being apparently absorbed 

 into the cytoplasm, while the remaining one (mic.") divides once 

 more, so that each conjugant has now again two micronuclei 

 (Fig. 41, D). These two, though similar in appearance, differ 

 strikingly in their behaviour, one of them remaining quiescent 

 while the other passes over into the body of the other conjugant. 

 They are therefore known respectively as the stationary (st.) and 

 the migratory (mig.) micronuclei. In this way the migratory 

 micronuclei of the two conjugants change places with one another, 

 as indicated by the arrows, and the sole object of the temporary 

 union of the two conjugants appears to be to enable this inter- 

 change to take place. When it has been effected a true conjuga- 

 tion occurs between the two micronuclei in each cell (Fig. 41, E, 

 gam.), derived one from each conjugant. This is the real sexual 

 process. The migratory and stationary nuclei are gametic nuclei 

 and the result of their union is a zygote nucleus (Fig. 41, F, zyg.\ 

 Moreover, we have here again an evident distinction into 

 male and female gametic nuclei, characterized in the usual 

 way by the activity of the one and the passivity of the other. 

 The two conjugants themselves, however, cannot be distin- 

 guished as male and female, for each produces both male 

 and female gametic nuclei and may therefore be regarded as 

 hermaphrodite. 



After the interchange of gametic nuclei has taken place the two 

 conjugants separate as ex-conjugants (Fig. 41, F). The zygote 

 nucleus in each divides repeatedly by mitosis and from the 

 daughter nuclei thus produced both micronuclei and meganuclei 

 are formed. Presently the ex-conjugants themselves begin 

 to divide once more by fission and the new micronuclei 

 and meganuclei are distributed amongst the new individuals 

 (Fig. 41, G). 



The essential feature of this very complicated process is clearly 

 the same as in the simpler cases which we have examined, and 

 consists in the union of two nuclei belonging to different cells to 



