Chapter 5 

 Reproduction 



THE mode of reproduction in Protozoa is highly variable 

 among different groups, although it is primarily a cell divi- 

 sion. The reproduction is initiated by the nuclear division in all 

 cases, which will therefore be considered first. 



Nuclear division 



Between a simple direct division on the one hand and a com- 

 plicated indirect division which is comparable with the typical 

 metazoan mitosis on the other hand, all types of nuclear division 

 are to be encountered. 



Direct nuclear division. While not so widely found as it was 

 thought to be in former years, amitosis occurs normally and regu- 

 larly in many forms. The macronuclear division of the Ciliophora 

 is without exception direct. The macronucleus elongates itself 

 without any particular changes in its internal structure and be- 

 comes divided through the middle, resulting in formation of two 

 daughter nuclei as seen commonly in Paramecium (Fig. 48). 



It is assumed that the nuclear components undergo solation 

 during division, since the formed particles of nucleus which are 

 stationary in the resting stage, manifest a very active Brownian 

 movement as was observed m vivo in Endamoeha hlattac (Fig. 49). 

 Furthermore, in some cases the nuclear components may undergo 

 phase reversal, that is to say, the chromatin granules which are 

 dispersed phase in the non-staining fiuid dispersion medium in 

 the resting nucleus, become dispersion medium in which the 

 latter is suspended as dispersed phase. By using Feulgen's nucleal 

 reaction, Reichenow (1928) demonstrated this reversal phenome- 

 non in the division of the macronucleus of Chilodonella cucullulus 

 (Fig. 50). 



When the macronucleus is elongated as in Spirostomum, 

 Stentor, Euplotes, etc., the nucleus becomes condensed into a 

 rounded form prior to its division. When the macronuclear ma- 

 terial is distributed throughout the cytoplasm as numerous grains 

 as in Dileptus anser (Fig. 239, c), "each granule divides where it 

 happens to be and with the majority of granules both halves 



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