124 



THE PROTOZOA 



C. The Nucleus 



Inclosed in the protoplasm in all Mastigophora is a more or less 

 clearly defined nucleus. It is variable in position, and although a 

 multiple number may occur, is generally single. The structure also 



tf W. 3S » 



t . s 



to 



» 6 

 • I « 



K6 



— s- 



m 



i £ 



rj 



^Wmm 



V 7 \ 





C 



^Mkrs, . . ■. ' . :r - 



W$0f/ 



Fig. 70. — Nuclear division in Noctiluca miliaris. 

 A. The first changes of the chromatin from the large karyosome condition ; concentration of the substance of the divi- 

 sion centre (s). B. Further disintegration of the chromatin and arrangement of granules to form the chromosomes {ch). 

 C. Amphiaster and completed chromosomes. D. The central spindle in the hollow of the nucleus; the nuclear plate of 

 chromosomes is thus wrapped around the division-centre. £. A section through the centre of the long axis of the division- 

 centre before division of the chromosomes. F. A section through the dividing chromosomes, c, the centrosome with 

 radiating mantle-fibres. 



is extremely variable. The chromatin may be either in the form of 

 granules distributed throughout the cell and not confined by a distinct 

 nuclear membrane ( Tetramitus), or the granules may be aggregated 

 without a membrane (Chilomonas), or again, the chromatin may be 



