12 



ESSENTIALS OF ZOOLOGY 



Paramecium. Of these two nuclei, one in each migrates into 

 the other Paramecium and fuses with the one which has not 

 migrated. The remaining nuclei which have been formed 

 during these changes, and the macronucleus in each case, all 

 gradually disappear. The single nucleus in each Paramecium 



Conjugation 



Transverse 

 fission 



FIG. 5. Reproduction of Paramecium. Diagrams to illustrate 

 transverse fission and the nuclear changes which take place 

 during conjugation. (After Delage and Herouard.) 



resulting from the fusion yields the micronucleus and the 

 macronucleus after the process has been accomplished. Then 

 the two Paramecia separate and begin a fresh series of trans- 

 verse divisions. 



Paramecium and other Ciliates have the power of encyst- 

 ment. The cell becomes rounded, the cilia are withdrawn, 

 and the surface secretes a gelatinous substance which hardens. 

 They are also liable to desiccation, and in such a state are 

 carried with the dust and spread into other and sometimes, it 



