PROTOZOA 



25 



process. The division centre may be intranuclear or extranuclear ; 

 when it is an extranuclear centriole, it is often identical or associated 

 with the basal granule of a flagellum. Cases in which the chromosomes 

 are distinct and on the whole behave like those of metazoa are known 

 as eumitoses. Another set of mitoses, known as paramitoses (Fig. 19), 

 differ from those of the Metazoa in that the chromosomes do not 

 shorten in the metaphase, and are not symmetrically arranged on the 

 equator of the spindle (if such be visible); and their longitudinal 



Fig. 20. Stages in the mitosis (cryptomitosis) of Haplosporidium limnodrili. 

 After Granata. A, Resting nucleus : the spindle here persists. B, Metaphase. 

 C, Anaphase. D, Telophase, clir. chromatin; kar. karyosome; spd. spindle. 



halves, when they separate, hang together to the last at one end so 

 that they appear, though deceptively, to divide transversely. In a 

 third set, known as cryptomitoses (Fig. 20), there are no distinct 

 chromosomes but the chromatin merely concentrates as a mass upon 

 the equator of a spindle, whose fibres may not be visible, and divides 

 into two halves which travel to opposite poles. Intermediate cases 

 connect cryptomitoses with eumitoses. Paramitoses occur in cocci- 

 dians, dinoflagellates, and the spore formation of radiolarians, crypto- 

 mitoses for the most part in parasitic and coprozoic forms, as in 

 Haplosporidium and Naegleria. 



