134 On the Genetics of the Ciliate Protozoa 



individual's micronucleus (or one of them in a multimicronucleate 

 form) now undergoes two' successive mitotic divisions, forming thus 

 four micronuclei (Fig. 2, B). Three of these four nuclei degenerate 

 (Fig. 2, B, C) and the remaining one again divides into two — a 

 "stationary nucleus" (s.n.) and a "migratory nucleus" (in.v.). Each 



mn I 



rn 71 2 



D 



n 



Fig. 2. 



migratory nucleus now passes into the opposite individual of the pair, 

 and fuses with its stationary nvieleus (Fig. 2, C, D, E). Each individual 

 thus comes to have a single micronucleus (z.n.) which is the product 

 of its own stationary nucleus and the migratory nucleus of its partner 

 (Fig. 2, E). The two organisms now separate, and their meganuclei 

 degenerate and disappear (Fig. 2, E). At the same time, the micro- 

 nucleus (fusion nucleus, s.n.) divides thrice in succession — producing 

 eight daughter nuclei (Fig. 2, E, F) in each individual. Of these eight 

 nuclei four increase in size, becoming new meganuclei, four remain 

 small as new micronuclei (Fig. 2, F, G). By two successive transverse 

 fissions of the whole organism, four small individuals are subsequently 

 formed (Fig. 2, G, H), each with the nuclear arrangement characteristic 



' In souie forms tliree or more such divisions occur. 



