10 



NORMAL HISTOLOGY. 



SYNOPSIS OF MITOTIC DIVISION. 



I. Prophases : 



A, Changes within the nucleus: Chromatic figure. 



Chromatin loses reticular arrangement. 

 Close skein. 

 Loose skein. 



Disappearance of nucleolus. 

 Division of skein into chromosomes. 

 Chromosomes grouped around polar field. 

 Disappearance of nuclear membrane. 



B. Changes within the cytoplasm : Achromatic figure. 



Division of centrosome. 



Appearance of asters. 



Migration of centrosomes. 



Formation of amphiaster. 



Appearance of nuclear spindle and polar field. 



II. Metaphase : 



Longitudinal cleavage of chromosomes. 



III. Anaphases : 



Rearrangement of chromosomes into two groups.- 

 Migration of groups towards poles of amphiaster. 

 Appearance of connecting fibres between receding groups. 

 Construction of daughter nuclei. 



IV. Telophases : 



Constriction of cell-body at right angles to axis of spindle. 

 Chromosomes rearranged as daughter skeins. 

 Appearance of nuclear membranes. 

 Appearance of nucleoli. 

 Complete division of cell-body. 

 Daughter nuclei assume vegetative condition. 

 Achromatic striation usually disappears. 

 Centrosomes, single or double, lie beside new nuclei. 



Amitotic Division. The occurrence of cell reproduction without 

 the complex cycle of karyokinetic changes, is known as amitotic or direct 



division. While an exceptional method, ami- 

 totic division is now recognized as of far wider 

 occurrence than formerly, particularly in 

 tissues, like fcetal membranes and tumors, 

 where temporary or abnormal cells are pro- 

 duced. The essential difference between the 

 direct and the usual method of division lies 

 in the fact that the amitotic process results in 

 mass-division of the nucleus without insuring 

 the equal apportionment of the chromatin or 

 the continuance of the normal quota of 

 chromosomes, as is accomplished by the 

 mitotic cycle. Neither the chromatic figure 

 nor the achromatic spindle is produced and 

 the influence of the centrosome is uncertain. The division of the cytoplasm 

 often lags behind that of the nucleus; consequently, the frequent production 

 of giant cells with multiple nuclei. It has been suggested that interference 



FIG. 7. Decidual cells exhibiting 

 amitotic division of nucleus (A-D); 

 in E irregular mitosis has occurred. 

 X ?5- 



