II 



Reproduction and Life-Cycles 



Methods of reproduction 

 Binary fission 

 Budding and schizogony 



Nuclear division 



Eumitosis and paramitosis 

 The micronucleus of ciliates 

 The achromatic figure 

 The macronucleus 



Life-cycles 



General features 

 Cysts 



Encystment 

 Excystment 



Sexual phenomena 



Varieties of sexual phenomena 

 Meiosis in relation to the life-cycle 

 Syngamy 

 Pedogamy 

 Autogamy 

 Conjugation 



Factors inducing conjugation 

 Mating types in ciliates 

 Nuclear phenomena of uncertain sig- 

 nificance 



The physiological life-cycle 



Literature cited 



I 



,N iMANY Protozoa, reproduction occurs at frequent intervals, 

 with relatively short periods of growth intervening under favorable con- 

 ditions. In other cases, growth may extend over a period of several to 

 many days, so that reproduction occurs at comparatively long intervals. 

 Depending upon the species, reproduction may or may not be preceded 

 regularly by sexual phenomena. Of the species which do show sexual 

 activity, some normally undergo syngamy as a prelude to a reproductive 

 phase while others show sporadic sexual activity. 



METHODS OF REPRODUCTION 



The less complex Protozoa reproduce either by binary fission or 

 by simple budding. In either case, the nucleus undergoes mitosis; or 

 mitosis of the micronucleus and "amitosis" of the macronucleus occur in 

 Ciliophora. Cytoplasmic division is approximately equal in fission, un- 

 equal in budding. 



Although reproduction in uninucleate species is comparable in some 

 respects to cell division in higher organisms, the structiual specialization 

 of many Protozoa introduces complications. The new organisms must be 

 equipped with various organelles, the nature of which varies with the 



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