50 



finer soluble wastes are discharged by the contractile 

 vacuoles. 



What happens when a Drop of Corrosive Sublimate Solution 

 is added to the Water containing Paramecium ? 



\ The trichocysts (in the cortex or ectoplasm) suddenly 

 extrude their long stinging threads, which are then seen 

 amongst the cilia. 



What is the special Importance of the Micronucleus in Para- 

 mecium ? 



It is the nucleus chiefly concerned in reproduction. 



How does Paramecium reproduce ? 



When full grown, it reproduces by simple transverse 

 binary fission. After a succession of generations by that 

 method, temporary conjugation occurs between two in- 

 dividuals and an exchange of micronuclear substance 

 takes place. 



Write a short Account of the Process of Conjugation in 

 Paramecium. 



Two Parameciums, which have degenerated in size arid 

 in other respects, approach each other and, side by side, 

 partly unite, their oral regions becoming fused and in- 

 distinguishable. In each the micronucleus undergoes 

 great change, increases in size, divides into two, then into 

 four. The four then proceed to divide again ; but three 

 are absorbed and only one completes the process, dividing 

 into two pronuclei, Each Paramecium has now two pro- 

 nuclei and one meganucleus (as yet unchanged). TJie 

 Parameciums now exchange each a pronucleus, and thus 

 an interchange of micronuclear substance is brought about. 

 The exchanged or migratory pronucleus fuses with the 

 stationary or retained one to form the zygote nucleus 

 (syngamy). Then the Parameciums separate. In each 

 the large meganucleus breaks up and disappears, and the 

 zygote nucleus undergoes three successive mitotic divisions, 



