i STRUCTURE AND PHYSIOLOGY OF ANIMALS 17 



one of the centrosomes and half towards the other (Fig. 3, F, G, H), 

 so that they are now separated into two- distinct groups. When the 

 groups have approached the extremity of the spindle, the 

 segments of each unite, and eventually the entire chromatin of 

 each of the two groups assumes the arrangement which the 

 chromatin of the original nucleus exhibited before jiiviion bggan, 



\ chr 



\ 



X G 



H 









FIG 3. Diagrams illustrating karyokinesis. A, the resting cell ; B, C, D, successive phases in 

 the formation and arrangement of the chromatin loops and of the nuclear spindle ; E, F, G, 

 separation of the two sets of daughter-chromosomes and their passage towards the poles of 

 the spindle ; II, 1, division of the cell-body and formation of the two new nuclei ; c. centro- 

 some ; </<;. chrnmatin ; </</. cell-plate ; iii'i nnaleoli ; nc . ///. nuclear membrane ; s. astrosphere ; 

 sp. spindle (From Parker's Biology, after Flernming, Rabl, &c.) 



A new nuclear membrane becomes formed around each chromatin 

 group, and the whole assumes the character of a complete nucleus 

 the daughter-nucleus. A furrow which appears on the surface of 

 the cell-protoplasm (Fig. 3, H, I), surrounding it in the form of a 

 ring in a plane at right angles to the long axis of the spindle, 

 deepens gradually so as to give rise to a cleft, eventually com- 

 pletery separating the substance of the cell into two halves. Each 

 VOL. i c 



