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 



(ft 



_-' E 



D 



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 

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

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

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

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

 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 



