FIG. 43. Stages in the division of Polytomella agilis. A, Resting condition of the 

 cell ; the four flagella arise from four blepharoplasts which are connected 

 by a rhizoplast with the nucleus ; in the nucleus is seen a large karyosome, 

 which contains the centriole and is surrounded by a peripheral zone of 

 chromatin-grains in a nuclear reticulum. B, Early stage of mitosis ; the karyo- 

 some is dividing to form a bar of chromatin occupying the axis of the achro- 

 matinic spindle, at the equator of which a plate of chromosomes is formed 

 by the peripheral chromatin of the last stage. C, Later stage ; the karyosome 

 has divided completely, forming two masses at the poles of the spindle con- 

 nected by a centrodesmose. D, The spindle has become elongated, and the 

 equatorial plate has split ; the centrioles are seen connected by the centro- 

 desmose. E, Division advancing ; the polar masses have become cap-shaped, 

 and the daughter-plates of chromosomfes have fused into conical masses ; 

 centrioles and centrodesmose still visible. F, Division of body beginning. 

 G, Centrodesmose broken through, the two daughter-nuclei separate. //, /, J, 

 Division of cell complete, one daughter-cell only represented, to show the 

 reconstitution of the daughter-nucleus ; the polar cap becomes the karyosome, 

 enclosing the centriole ; the conical mass formed in Stage E by fusion of the 

 chromosomes in the daughter-plates becomes resolved gradually into 

 chromatin-grains again, and so forms the peripheral zone of the daughter- 

 nucleus ; each daughter-cell has two of the four blepharoplasts and flagella 

 of the parent, and the number is doubtless made up to four again by division 

 after the daughter-cells are set free. After Aragao (45). 



