Reproduction and Life-Cycles 



65 



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Fig. 2. 7. Mitosis in Pcloinyxa caroUnensis. A. Interphase; x2300. B. 

 Early prophase; x2300. C. Late prophase; x2645. D, E. Separation of daugh- 

 ter chromosomes; x2990. F. Chnnping of chromosomes in late anaphase; 

 x2990 (after Kudo). 



and in Euglenida and Dinoflagellida. The appearance of Y-shaped daugh- 

 ter chromosomes during anaphases, as described in PleurotricJia lanceo- 

 lata (173), would suggest median instead of terminal centromeres. 



Persistence of the nuclear membrane throughout mitosis is character- 

 istic of many Protozoa. However, a large portion of the old membrane is 

 discarded after division of the nucleus in Holomastigotoides (63) and 

 disappearance of the membrane in the prophase has been described in 

 Dimorpha mutatis (20). 



The micronucleus of ciliates 



The small size of the micronucleus increases the difficulty of inter- 

 preting chromosomal behavior. Longitudinal splitting of the chromo- 

 somes has been reported in some species and transverse division in others, 

 but decisions are difficult for the almost spherical chromosomes found in 

 certain ciliates. Longitudinal splitting has been described in Pleurotricha 

 (173), Stylonychia (119a), Concliophtliirius (144), and in pregamic di- 

 visions in Euplotes (234). In the last three cases, members of each pair 

 of daughter chromosomes slip past each other toward the poles of the 

 spindle (Fig. 2. 9). 



