FERTILIZATION 



257 



B 



D 



E 



H 



I 

 J 



K 

 L 



Fig. 170. — Diagram of the nuclear changes during fertilization (conjuga- 

 tion) in Paramecium aurelia. A, union of two individuals along the peristomal 

 region; B, degeneration of macronucleus and first division of the micronuclei; 

 C, second division of micronuclei; D, seven of the eight micronuclei in each 

 conjugant degenerate (indicated by circles) and disappear; E, each conjugant 

 with a single remaining micronucleus; F, this nucleus divides into a stationary 

 micronucleus and a migratory micronucleus — the gametic nuclei. The mi- 

 gratory micronuclei are exchanged by the conjugants and fuse with the re- 

 spective stationary micronuclei to form the synkarya. This is fertilization. 

 G, conjugants, with synkarya, separate (only one is followed from this point); 

 H, first division of synkaryon to form two micronuclei; I, second reconstruc- 

 tion division; J, transformation of two micronuclei into macronuclei; K, divi- 

 sion of micronuclei accompanied by cell division; L, typical nuclear condition 

 restored. 



