66 



CELL-DIVISION 



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

 Actinospharium % 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. 



*s&t 



Fig. 31. Mitosis in the rhizopod Actinospharium. [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. D. 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 en face, consisting of double chromntin-granules. E. Early anaphase. F. G. Later ana- 

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

 threads; outside the nuclear membrane the cenirosome, already divided, and the aster. J. Lnter 

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

 centrosomes have not been followed. 



Only in the late anaphase (telopJiase) do these grannies arrange thcm- 

 selves in threads (Fig. 3 1, /), 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. 



