SPECIAL MORPHOLOGY OF THE PROTOZOAN NUCLEUS 



2/1 



in Euglena, the intra-nuclear division-centre dividing first. After 

 division the chromatin granules again disperse and the division-centre 

 becomes again cytoplasmic (Fig. I43). 1 



Still more convincing evidence is shown by the history of the 

 division-centres of Acanthocystis and the flagellate Oxyrrhis marina 

 (Schaudinn, '96). Acanthocystis has a permanent extra-nuclear division- 

 centre which divides and forms a complete spindle (Fig. 144, A-D). 



B 



Fig. 144. Nuclear division and spore-formation in Heliozoa. [SCHAUDINN.] 

 A, A vegetative cell of Sphczrastrum with the axial filaments focussed in a central-granule 

 (division-centre). B-D. Division of the nucleus in Acanthocystis. E,F. Flagellated and amoe- 

 boid swarm-spores formed by budding. G. Exit of the division-centre from the nucleus. 



Like Paramceba this heliozoon reproduces by swarm-spores ; the 

 division-centre, however, takes no part in their formation, but remains 

 intact while the nucleus divides without mitosis. The buds, therefore, 

 contain no portion of the original material of the division -centre, nor is 

 there any evidence in them of such a centre until about the fifth day. 

 At this time Schaudinn found a " Centralkorn " within the nucleus of 

 each swarm-spore, which passed later through the nuclear membrane 

 and into the cytoplasm, where it developed into the well-known divi- 

 sion-centre of the adult Acanthocystis (G). 



The extrusion of the kinetic substance of the nucleus which thus 



J An intermediate stage between this condition and the condition in Euglena is shown by 

 some species of Chilomonas and Trachelomonas, in which there is no nuclear membrane, 

 but in which the chromatin remains permanently aggregated about the division-centre 

 (Calkins, '98). 



