THE ANAPHASES. DIVERGENCE AND SEPARATION OF THE DAUGHTER-CHROMOSOMES. 27 



Plate VIII. Phototype 31. 

 Later Anapliasc\ showing especially the Chromosomes. 



The section passes slightly to one side of the spindle-axis, and hence does not show the achromatic figure as 

 well as the last or the following. The chromosomes are, however, very clearly shown, and they may be seen to 

 correspond accurately on the two sides, each daughter-chromosome having its fellow on the opposite side (cf. Text-fif. 

 XVI. B). Observe the very considerable variation in size, and also the varying intervals between the halves of each 

 pair. The latter fact shows that the chromosomes move to some extent independently of one another. 



Stretching between the two groups of daughter-chromosomes, in the equatorial region of the spindle, may 

 be seen spindle-fibres, known as the " interzonal fibres " (" filaments reunissants," " Verbindungsfasern "), regarding 

 which much discussion has arisen (I.F. in Text-fig. V. C). According to Hermann they are non-contractile and 

 form a "central spindle" alon ■; which the chromosomes are dragged, the contractile fibres forming the peripheral 

 portion of the spindle ("Spindle-mantle"). As will appear beyond, there is no ground in Toxopneustes iox vi\-^6.vi^ Ti^ny 

 distinction between these fibres and the others. 





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B ' I \-\- 



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Fig. XVII. — The closing stages of Uaryokinesis (looo iliameters). 



A. I.ate anaphase. The riaughter-chromosomes have passed to the spindle-poles and lie in contact with the reticular centrosphere. Central portion of the spindle breaking up to 



form the " Zwischenkorper," or mid-body (Phototype 32). 



B. The chromosomes have become converted into vesicles. The centrosphere very large, its borders vague and indistinct. (Phototype 34.) 



Plate VIII. Phototype 32. 

 Late Anaphase. Complete Divergence of the Daughter-chromosomes. 



The daughter-chromosomes have now passed outwards to the extreme limit of the spindle and lie in contact 

 with the centrosphere. Were their movements due to the action of contractile fibres, the thickened fibres should 

 appear between them and the centrosphere. No such fibres are present, however, and the movements must therefore 

 have some other cause. 



The achromatic figure is now nearly at a ma.ximum. The centrospheres are very conspicuous, and their reticular 

 substance is clearly shown. The aster consists of an inner denser zone, composed of close-set granular rays, and a 

 peripheral looser portion composed of long rays extending far out into the general reticulum, the meshes of which are 

 here very plainly shown. 



The equatorial region of the spindle is becoming disorganized, the fibres breaking up into rather coarse blue granules 

 which, at a later stage, form a body known as the " Zwischenkorper," or mid-body. 



