DETAILS OF MITOSIS 



8i 



origin, since the ends of the spindle begin to form before dissolution 

 of he nuclear membrane, and the latter is pushed inwards in folds 

 by the mgrowing fibres (Figs. 25, C, 99)-^ In some cases, however 

 It seems certain that the nuclear membrane fades away before com- 

 pletion of the spindle (first maturation-division of Thalassema, ChcE- 

 topterus\ and It is probable that the middle region of the spindle is 

 here formed from the linin-network. In most, if not all, mitoses of 

 the second type the chromosomes do not form a ring about the 

 equator ot the spindle, but extend in a flat plate completely throuo-h 



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Fig- 32. — Mitosis in Sfypocaulon. 

 A. Early prophase with single aster and centrosome. 



[Swingle.] 



:S5et.^ ^'— "^-^ -^— -='"- -^;si^rr£i;"r^ 



ts substance. Here, therefore, it is impossible to speak of a " cen- 

 tral spindle It IS nevertheless probable that the spindle-fibres are 

 ot two kmds, VIZ. continuous fibres, which form the interzonal fibres 

 seen during the anaphases, and half-spindle fibres, extending only 

 from the poles to the chromosomes. It is possible that these two 

 kinds of fibres, though having the same origin, respectively corre- 



Triion IlTcr-Jl^fl^"^ 'V'" ^f ,^'f"''^^/'^'-'^^ Watase ('91) on lo/i^o, Braus ('95) on 

 Irn 'osis o? fh ^ ^ ' ^^ "" f -^-— Erianger ('97, 5) endeavours to show 'hat in 

 the m.tosis of embryonic cells m the cephalopods (Sepia), where the inpushing of the mem- 

 brane was previously shown by Watase. the entire spindle arises from the nucleus 

 a 



