CELL DIVISION 



17 



these groups there is a longitudinal half of each of the 

 chromosomes that originally appeared. While the chromo- 

 somes are thus separating, the whole cell gradually assumes 

 an hour-glass shape (Fig. 8), and this becomes more and 

 more accentuated until the original mass of protoplasm, 

 that is, the cell, is divided into two at the narrow point 

 in the centre (Fig. 9). We thus have two masses of proto- 

 plasm produced from the original single mass, and each 

 of these two masses contains an exact longitudinal half of 

 every chromosome that appeared during the preparation for 

 division in the mother cell. Each chromosome in the group 

 surrounding the centrosome in the daughter cell now pro- 



FIG. 10. Commencement of 

 reconstruction of daughter 

 nuclei. 



FIG. 11. The two daughter 

 cells complete. 



ceeds to throw out small processes which join the chromo- 

 somes to each other, and a new nuclear membrane is formed 

 (Figs. 10 and 11). The shapes of the chromosomes are gradu- 

 ally lost, and as the processes of linin form a network within 

 the new nucleus, the chromatin is gradually distributed 

 through this network, and the nucleus of the daughter cell 

 assumes the appearance that was described in the case of 

 the mother cell. The single centrosome which has been 

 received into the daughter cell divides into two, as a rule, 

 very soon after the nuclear membrane has been formed, but 

 unless another division is imminent these two centrosomes 

 remain quiescent for a time. 



B 



