CH. II.] 



CELL DIVISION. 



The changes in the nucleus during indirect division constitute 

 karyokinesis (KOJIVOV, a kernel), or mitosis (/WTO?, a thread), and 

 direct division is called amitotic or akinetic (KOT^IS, movement). 

 It is now believed that the mitotic nuclear division is all but, though 

 not quite, universal. Somewhat different accounts of the stages 

 of the nuclear division have been given by different authorities, 

 according to the kind of cell in which the nuclear changes have 

 been studied. The following will summarise the stages of karyo- 

 kinesis as observed by Klein : 



The nucleus in a resting condition, i.e., before any changes 



Fig. 1 8. Karyokinesis. A, ordinary nucleus of a columnar epithelial cell ; B, c, the same 

 nucleus in the stage of convolution ; D, the wreath or rosette form ; E, the aster, or single 

 star ; y, a nuclear spindle from the Dcscemet's endothelium of the frog's cornea ; 

 o, H, i, diaster ; K, two daughter nuclei. (Klein.) 



preceding division occur, consists of a very close mesh work of fibrils, 

 which stain deeply with carmine, embedded in a matrix, which 

 does not possess this property, the whole nucleus being contained 

 in an envelope. The first change consists of a slight enlargement 

 of the nucleus, the disappearance of its envelope and an increase in 

 the definition and thickness of the nuclear fibrils, which are also 

 more separated than they were, and stain better. This is the 

 stage of convolution (fig. 18, B, c). The next step in the process 

 is the arrangement of the fibrils into some definite figure by an 

 alternate looping in and out around a central space, by which 

 means the rosette or wreath stage (fig. 18, D) is reached. The 

 loops of the rosette next become divided at the periphery and 

 their central points become more angular, so that the fibrils, 

 divided into portions of about equal length, are doubled at an 

 acute angle, and radiate in a V-shaped manner from the centre, 

 forming a star (aster) (fig. 18, E), and later from t\vo centres, 



