THE CELL AND THE TISSUES. 



delicate striae make their appearance, so disposed that together they 

 present a double cone, whose apices are directed towards the poles 

 of the future new nuclei, and whose bases are placed centrally and 

 occupy the polar field; these achromatin figures constitute the nu- 

 clear spindle. The chromatin fibrils grow thicker and, at the 

 same time, shorter, and arrange themselves so that the closed ends 

 of the loops encircle the polar field, giving rise, when seen from its 

 surface, to the wreath; seen from the side, however, the loops or V's 

 appear as radiating fibrils, and constitute the 



(4) Mother-star, or aster: the apparent differences, therefore, 

 between the wreath and the aster depend upon the point of view, 

 and not upon variations in the arrangement of the fibres. Another 

 very important change is now observed. 



(5) Each of the loops undergoes longitudinal cleavage, split- 

 ting up into double the number of segments: these are now entirely 

 rearranged, the first step being 



(6) A rapid separation into two groups, passing towards the poles 

 of the future new nuclei, as indicated by the foci of the nuclear 

 spindle. Around these points as centres, a deli- 



cate radial marking the polar striation ap- 

 pears. The halves of the longitudinally-cleft 

 fibrils are so disposed that one of each pair of 

 sister-segments passes along the guiding lines of 

 the achromatin spindle to each of the groups, thus 

 insuring an accurate and equal division of the 

 original chromatin between the new nuclei. The 

 chromatic segments, becoming further aggregated 

 about the equator of the nuclear spindle in their 

 migration, form a compressed mass, known as the 



(7) Equatorial plate.* As the newly-grouped 

 fibrils pass outward towards their respective poles, 

 the free ends of the receding segments become 

 united by delicate threads of achromatin the 

 connecting filaments which stretch between 

 the corresponding limbs of the separating seg- 

 ments. With the completion of migration the 

 cardinal features of the division of the nucleus 

 have been established, since the subsequent 

 stages are but repetitions, in inverse order, of the 

 changes already instituted. Following the stage 



of the equatorial plate, the fibrils group themselves about the poles 

 of the spindle and form 



* The term "equatorial plate" has been employed by some authors to indicate 

 the later phases of the aster stage. 



GP 



Rearrangement and 

 cleavage of V-segments : 

 A , from the side ; B. 

 from the polar field, P ; 

 GP, anti-pole. (After 

 Rabl-Schieffer decker.) 



