REPRODUCTION 



179 



three times (Fig. 138, //-J), resulting in the formation of eight micronuclei. 

 Of these, four are segregated and become macronuclei, three of the re- 

 mainder degenerate, and one continues as a micronucleus which soon 

 divides. The ex-conjugant which now has four macronuclei and two 

 micronuclei then divides (M, iV), each new individual receiving one micro- 



A/ 



N 



Fig. 138. — Diagram showing sequence of nuclear changes during and following con- 

 jugation in Paramecium. A-P, successive stages. The dotted bodies represent degenerat- 

 ing nuclei; mn, macronuclei; n, micronuclei; n 9 , portion of micronucleus which remains in 

 same individual; ncf , portion of micronucleus which migrates to the other individual and 

 fuses with ?i 9 • During stages A-G the conjugating paramecia remain in contact; after 

 those stages they are separate. 



nucleus and two macronuclei. After a brief growth period the micro- 

 nucleus again divides and another division of the cell takes place, thus 

 leaving each cell with one macro- and one micronucleus. After another 

 growth period each cell divides by fission, and at intervals of 16 to 24 

 hours thereafter for a considerable period, when again conjugation usually 

 occurs. The part of this process which corresponds to fertilization is the 



