DETAILS OF MITOSIS 



93 



passes through a spireme-stage, breaks into very short rod-shaped 

 chromosomes which spHt lengthwise and arrange themselves in the 

 equator of the spindle, while the nuclear membrane fades away. 

 Noctiluca (Fig. 42), as shown by Ishikawa and Calkins, agrees with 

 this in the main points ; but the nuclear membrane does not at any 

 period wholly disappear, and a distinct centrosome is found at the 

 centre of the sphere. The latter body, which is very large, gives 



, '^^^'. 





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(«yt/i^;S 





D 



Fig. 42. — Mitosis in Noctiluca. [CaLKINS.] 

 A. Prophase; division of the sphere to form the central spindle; chromosomes converging; to 

 the nuclear pole. B. Late anaphase, in horizontal section, showing centrosomes; the central 

 spindle has sunk into the nucleus ; nuclear membrane still intact except at the poles. C. Early 

 anaphase; mantle-fibres connected with the diverging chromosomes. D. Final anaphase (which 

 is also the initial prophase of the succeeding division of spore-forming mitosis) ; doubling of cen- 

 trosome and splitting of chromosomes. 



rise by a division to a fibrillated central spindle, about which the 

 nucleus wraps itself while mantle-fibres are developed from the 

 sphere-substance and become attached to the chromosomes, the nu- 

 clear membrane fading away along the surface of contact with the 

 central spindle (Calkins). Broadly speaking, the facts are similar in 



