102 NUCLEAR DIVISION IN PROTOZOA 



essential features are the appearance in the karyosome of granules which 

 become irregularly arranged in longitudinal rows on the fibres which 

 appear in the elongating karyosome. Spindle fibres are thus produced, 

 but the chromatin granules do not unite to form chromosomes, nor is 

 an equatorial plate developed. Nothing in the nature of a centrosome 

 is present. 



The stages in the division of Amoeba hyalina (Hartmannella hyalina), 

 described by Hartmann and Chagas (19106), illustrate the type of division 

 in which a centriole is supposed to be present (Fig. 59). The resting 

 nucleus is described as having a centriole within the karyosome. When 



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Fig. 59. — Stages in Mitotic Division of Nucleus of Hartmannella hyalina, in 



WHICH it is supposed THAT A CeNTRIOLE FUNCTIONING AS A CeNTROSOME IS 



PRESENT (x 3,700). (After Hartmann and Chagas, 1910.) 



division commences the centriole divides, and as the two halves separate 

 they are connected by a centrodesmose. The chromatin of the karyosome 

 breaks up into granules, which become arranged as chromosomes in an 

 equatorial plate. Each daughter centriole has now taken up a position 

 at the apex of the spindle-shaped nuclear membrane, within w^hich is 

 a system of exceedingly fine spindle fibres. The daughter plates of 

 chromosomes are formed, and these move towards the poles of the spindle. 

 Finally, the chromosomes at each end run together to form the karyosome, 

 in which the centriole is included, while the intermediate part of the 

 spindle disappears. It is by no means clear that the above is an accurate 

 description. Other observers who have investigated the nuclear division 

 of this or similar amoebse have failed to detect the centrioles (Fig. 89). 

 Arndt (1924), in describing the nuclear division of HartmanneUa 



