PROTOZOA 29 
Fic, 21.—Paramoecium aurelia in process of conjugating. Maupas. 
1. The two paranuclei in each individual becoming spindle-shaped and com- 
mencing to divide. 
2. Stage with four paranuclei in each individual. 
3. The four paranuclei again divide. The division is almost complete in the left 
Paramoecium. 
4. Stage with eight paranuclei. 
5, Seven paranuclei being absorbed, and the one nearest the mouth remaining and 
dividing in two, the male and female pronuclei. 
6. Exchange of male pronuclei. 
7. The male has fused with the female pronucleus to form the fertilised paranucleus. 
8. The fertilised paranucleus divides. 
9. The resulting halves divide again. 
10. The two halves at the posterior end form the new paranucleus ; the two at the 
anterior end, the new nucleus. 
The disintegration and dissolution of the nucleus are shown in the same series of figures. 
