PARAMECIUM 



75 



four micronuclei thus produced three degenerate and disappear, and 

 the fourth divides again, this time unequally. The smaller of the two 

 micronuclei of each animal now moves over the protoplasmic bridge into 



777/5 animal 

 not followed 

 further; same 

 as other 



1. Two paramecia come together 



MicronucleiLs divides. Macronucleus begins to dis- 

 integrate 



3. Micronuclei divide and three of four disappear 



4. Remaining micronucleus divides unequally 



5. Smaller micronucleus crosses into other animal 



G. Each animal with its own larger micronucleus and 

 smaller one from other animal 



7. Two micronuclei fuse 



8. Two animals separate. Each exconjugant with 

 fusion micronucleus 



9. Fusion micronucleus divides 



10. Two micronuclei divide 



11. Four micronuclei divide 



12. Four micronuclei become macronuclei, three dis- 

 o#o#««o» ? appear, one remains 



13. Micronucleus divides and animal divides 



14. In each of two micro- 

 nucleus divides and ani- 

 mals divide again 



Fig. 24. — Diagram illustrating conjugation in Paramecium caudatum Ehrenberg. 

 (Siiahthj modified from Jennings, "Life and Death, Heredity and Evolution in Unicellular 

 Organisms," by permission.) Macronucloi are indicated by large black bodies, micronuclei 

 by the smaller ones, and those micronuclei which disappear by small circles. 



the other animal, passing the micronucleus from the other as it does so. 

 Each of these micronuclei fuses with the larger micronucleus of the other 

 animal, forming a fusion micronucleus. This process has been compared 



