130 Darwin, and after Darwin. 



form of a wreath (D), and subsequently (by the breaking of 

 the loops formed by the fibres) in the form of a star (E). A 

 further movement within the nucleus leads to an arrangement of 

 the broken loops in two groups (F), the position of the open ends 

 of the broken loops being reversed as compared with what pre- 

 viously obtained. Now the two groups diverge, and in many 

 cases a striated appearance of the achromatin substance between 

 the two groups of chromatin loops is observable (H). In some 

 cases (especially egg-ceils) this striated arrangement of the 

 achromatin is then termed a "nucleus-spindle," and the group of 

 chromatin loops (G, a) is known as " the equatorial plate." At each 

 end of the nucleus-spindle in these cases there is often seen a 

 star consisting of granules belonging to the general protoplasm 

 of the cell (G, c). These are known as " polar stars." After the 

 separation of the two sets of loops (H) the protoplasm of the 

 general substance of the cell becomes constricted, and division 

 occurs, so as to include a group of chromatin loops in each of the 

 two fission products. Each of these then rearranges itself to- 

 gether with the associated chromatin into a nucleus such as was 

 present in the mother cell to commence with (I) 1 . 



Since the above was published, however, further 

 progress has been made. In particular it has been 

 found that the chromatin fibres pass from phase D 

 to phase F by a process of longitudinal splitting (Fig. 

 37 g; h ; Fig. 38, VI, VII) which is a point of great 

 importance for Weismann's theory of heredity, and 

 that the protoplasm outside the nucleus seems to 

 take as important a part in the karyokinetic process 

 as does the nuclear substance. For the so-called 

 "attraction-spheres" (Fig. 38 II a, III, III a, VIII to 

 XII), which were at first supposed to be of subordinate 

 importance in the process as a whole, are now known 

 to take an exceedingly active part in it (see especially 

 IX to XI). Lastly, it may be added that there is a 



1 Ray Lankester, Encydop. Brit., gth ed., Vol. XIX, pp. 832-3. 



