CELL-DIVISION 



represents the centrosome alone. In other cases the granule is sur- 

 rounded by a larger body, which in turn lies within the centrosphere 

 or attraction-sphere. In still other cases the centre of the aster is 

 occupied by a large reticular mass, within which no smaller body can 

 be distinguished (e.g. in pigment-cells) ; this mass is sometimes called 

 the centrosome, sometimes the centrosphere. Sometimes, again, the 



Fig. 24. The middle phases of mitosis in the first cleavage of the Ascaris-egg. [BOVERI.] 



A. Closing prophase, the equatorial plate forming. B. Metaphase ; equatorial plate estab- 

 lished and the chromosomes split ; b, the equatorial plate, viewed en face, snowing the four chro- 

 mosomes. C. Early anaphase ; divergence of the daughter-chromosomes (polar body at one 

 side). D. Later anaphase ; p.b., second polar body. 



(For preceding stages see Fig. 65 ; for later stages, Fig. 104.) 



spindle-fibres are not focussed at a single point, and the spindle 

 appears truncated at the ends, its fibres terminating in a transverse 

 row of granules (maturation-spindles of Ascaris, and some plant-cells). 

 It is not entirely certain, however, that such spindles observed in 

 preparations represent the normal structure during life. 1 



1 Hacker asserts in a recent paper ('94) that the truncated polar spindles are normal, 

 and that a centrosome lies at each of the four angles; i.e. two at either pole. 



