390 



THE INFUSORIA 



(III., V.), break up into lumps (VI.), into smaller droplets, and 

 ultimately disintegrate (X.) and disappear (XL). 



The changes which take place in the cytoplasm during conjuga- 

 tion have not yet been followed in detail. There can be little 

 doubt that an interchange of molecules of cytoplasm between the 

 two individuals does occur, but it is quite impossible to tell 

 whether the mixing of the two cytoplasms is or is not complete. 



In the accounts given of the conjugation of the Ciliata, it is stated 

 that the meganucleus plays a perfectly passive role until its disintegration 

 begins. 



In Spirochona the meganuclei fuse during conjugation ; and in 

 Dendrocometes the meganuclei come in contact during conjugation, but 

 subsequently separate (Fig. 39). 



FIG. 



Reconstruction of a series of sections through a pair of conjugating Dendrocometes, showing 

 a temporary fusion of the two meganuclei (M ), at the conclusion of the process. MN, the 

 new meganucleus ; m, the three new micronuclei. (Original.) 



In those species which normally possess more than one micro- 

 nucleus the process is rather more complicated. 



In Paramoecium aurelia the two micronuclei which are normally 

 present in each individual divide twice, giving rise to eight nuclei, 

 of which number seven degenerate and one remains as the sexual 

 nucleus. After the conjugation of the migratory and stationary 

 nuclei, the cleavage nucleus of each individual divides twice, and 

 of the four nuclei thus formed, two directly give rise to meganuclei 

 and the remaining two divide again to give rise to the two micro- 

 nuclei in each of the daughter individuals formed by the first fission. 



In Dendrocometes there are usually three micronuclei in each 

 individual. At the commencement of conjugation all three micro- 

 nuclei enlarge and undergo mitosis (Fig. 40), but not simultaneously. 

 Of the six nuclei thus formed, five degenerate and one passes down 

 the junction and forms the sexual nucleus. 



In Bursaria truncatella there are, according to Prowazek, normally 

 1 6-.1 8 micronuclei in each individual, which give rise to no less than 



