66 



CELL-DIVISION 



figure, except the minute asters, is formed inside it (Fig. 28). In 

 ActinospJicerimn, on the other hand, there is no true spireme stage, and 

 no rod-shaped chromosomes are at first formed. The reticulum breaks 

 up into a large number of granules which give rise to an equatorial 

 plate, divide by fission, and are distributed to the daughter-nuclei. 



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Fig. 31. — Mitosis in the rhizopod ^t/ww/^«r2w;«. [BRAUER.] 

 A. Nucleus and surrounding structures in the early prophase ; above and below the reticular 

 nucleus lie the semilunar " pole-plates," and outside these the cytoplasmic masses in which the 

 asters afterward develop. B. Later stage of the nucleus. D. Mitotic figure in the metaphase, 

 showing equatorial plate, intra-nuclear spindle, and pole-plates {p.p.). C. Equatorial plate, 

 viewed e/t face, consisting of double chromatin-granules. E. Early anaphase. F. G. Later ana- 

 phases. H. Final anaphase. /. Telophase; daughter-nucleus forming, chromatin in loop-shaped 

 threads ; outside the nuclear membrane the centrosome, already divided, and the aster. J. Later 

 stage ; the daughter-nucleus established ; divergence of the centrosomes. Beyond this point the 

 centrosomes have not been followed. 



Only in the late anaphase {telophase) do these granules arrange them- 

 selves in threads (Fig. 31,/), and this process is apparently no more than 

 a forerunner of the reticular stage. This case is a very convincing 

 argument in favour of the view that the formation and splitting of chro- 

 mosomes is secondary to the division of the ultimate chromatin-granules. 



