ZOOLOGY 



two (8 and 9, and F), and each half divides again (G), so that 

 each individual contains four fragments of paranucleus : two at 

 one end of the hody and two at the other (9). The two at 



12 3 4 



Fig. 22. — Diagram of changes undergone by 

 paranuclei of Paramoecium aurdia during 

 conjugation. Maupas. 



A. Increase in size of paranuclei 



B. 1st division of paranuclei. 



C. 2nd division of paranuclei, and disappearance 

 of seven-eighths. 



D. Division of remaining portion into male and 

 female pronuclei. 



E. Fusion of male and female pronuclei. 



F. Division of fertilised paranucleus into two 

 halves, 



G. Division of these halves. 



H. Of the four quarters shown in G, one forms 

 the new nucleus of young Paramoecium which is 

 formed by fission, the other divides into two and 

 forms two paranuclei, one in each of the new indi- 

 viduals. 



the posterior end undergo no change, and form the paranuclei 

 of the new individuals which result from the subsequent 

 fission ; the two at the anterior end increase, and are destined 

 to form the nuclei of the new individuals (10). Before this 

 is completed, however, the two paranuclei have again divided 



Fig. 23. — Opalind rananim, Ehrb. 



1. Nuclei. 



2. Ectoplasm. 



From Bronn. 



(H), SO that after fission each new individual contains one 

 nucleus and two paranuclei. 



Whilst the paranucleus of the original Paramoecium has 

 been undergoing these changes, the nucleus has first become 



