OJikiiiosis ill ( 'crchral iiliis LiU-tens. 385 



Difference is 5.0*^5 microns. 



The eloniitition of the egg is 0,13 microns. 



From this it will be seen that the chromosomes move much faster 

 at this stage than the centrioles (cf. Ziegler, '95, p. 383). The lateral 

 stretching of the karvokinetic axis takes place later on. 



2. Spindle. 



At an early anaphase the spindle is convex in outline at the middle. 

 Approaching the telophase, however, the fibres straighten themselves, 

 the width of the spindle being consequently reduced to one half or 

 sometimes still less (Text Fig. C. 1-4). After the daughter nuclei 

 are formed, the spindle fibres are bent toward the vegetative i^ole 

 (Text Fig. C, 5). This bending is not due to the cell constriction, 

 because this takes place long before the cleavage furrow reaches the 

 spindle, and moreover against the pushing-in of the vegetative furrow. 

 In later stages, of course, the animal furrow accentuates the bend- 

 ing. It may be pointed out, therefore, that this common phenomenon 

 of spindle bending is an expression of protoplasmic movement."'' 



3. Centrosome. 



At the anaphase the centrosome is sausage-shape, placed hori- 

 zontally perpendicular to the spindle. At a late anaphase it flattens 

 and spreads out at the expense of the chromosomal fibres (Text Fig. 

 C. 4 — horizontal section). The nature of the centroplasm changes 

 from homogeneous to alveolar and now it does not appear so viscid 

 as it has been. The centrosome is gradually bent downward so that 

 the centrioles are no longer found on the same horizontal plane 

 as the spindle, but far below the latter (Text Fig. C 3). As I have 

 already mentioned, the spindle fibers by this time are curved toward 

 the vegetative pole and the karyokinetic axis, therefore, takes the 

 form of an inverted W (Text Fig. C. 5). Later the nucleus too 

 yields to the shape of this curve. The centrioles go to the extreme 

 end of the centrosome, where \hc\ acquire new ray systems. Often 



■-"It is noteworthy that in the esg of PcdiceUina americana the spindle of the 

 first cleavage is hent towards the animal jwle, as I was informed hy Dr. 

 Dublin. 



