THE PROTOZOA 



The two individuals that are going to conjugate, and may 

 therefore be termed the conjugants, do not differ structurally from 

 other individuals, but perhaps they are slightly smaller. They 

 come together by their oral or ventral surfaces and adhere by their 

 anterior halves. The micronucleus in each enlarges and undergoes 

 indirect division similar to that in binary fission. The daughter 

 nuclei similarly divide so that four micronuclei are produced in each 

 cell, one of which, the one that happens to lie nearest the peristoir t e, 

 persists, while the three remaining ones break up and are gradually 

 absorbed by the cytoplasm. While they are disappearing the 

 remaining micronucleus again divides into two. The one lying 



FIG. 42. Diagram of conjugation in Paramcecium, to show the nuclear 

 changes. The position and size of the nuclei are purely diagrammatic. 



A. B. ( conjugants ; C. D., ex-conjugants. 



further from the cytostome we distinguish as the stationary nucleus, 

 because it remains behind in the cell that produced it. The other, 

 nearer to the cytostome, is the migratory nucleus, and is destined 

 very shortly to pass over into the other conjugant. When this 

 happens each individual possesses two micronuclei, one descended 

 from its own original micronucleus and the other that has migrated 

 into it. These two nuclei fuse together and give rise to the conjuga- 

 tion nucleus, and then the two conjugants separate from one another. 

 We have thus as the essential part of conjugation the fusion of 

 nuclear material derived from two distinct individuals, and it will 

 be remembered that a somewhat similar fusion is characteristic 

 of the phenomenon known as fertilisation in the Metazoa. 



