14 



HUMAN ANATOMY 



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 appears at right angles to spindle, 



Chromosomes rearranged in daughter nuclei to form skeins. 



Reappearance of nuclear membrane, 



Reappearance of nucleoli. 



Complete division of cell-body. 



Daughter nuclei assume vegetative condition, 



Achromatic striation usually disappears, 



Centrosomes, single or divided, lie beside new nuclei. 



v 



cleavage of 

 vidual 



AMITOTIC DIVISION. 



The occurrence of cell reproduction without the foregoing complex cycle of 

 karyokinetic changes is known as a^nitotic or direct division. That this process does 

 take place as an exceptional method in the reproduction of the simplest forms of ani- 

 mal life, or in the multiplication of cells within pathological growths or tissues of a 



transient nature, as the fcetal envelopes, may 

 Pig. io. be regarded as established beyond dispute. 



The essential difference between amitotic 

 and the usual method of division lies in the 

 fact that, while in the latter the chromatin of 

 the nucleus is equally divided and the number 

 of chromosomes carefully maintained, in direct 

 division the nucleus remains passive and suffers 

 its total mass, but not of its indi- 

 components. Since the nucleus re- 

 mains in the vegetative condition, neither 

 the chromatic nor achromatic figure is pro- 

 duced, the activity of the centrosome, when 

 exhibited, being possibly directly expended in 

 effecting a division of the cytoplasm, and inci- 

 dentally that of the nucleus. In many cases 

 the amitotic division of the nucleus is not ac- 

 companied by cleavage of the cytoplasm, such 

 processes resulting in the production of multi- 

 While in general, it may be assumed that cells 

 which undergo direct division are elements destined to suffer premature degeneration, 

 the studies of Child have shown that amitotic division is of much wider occurrence 

 than formerly recognized; further, that due to changes of environmental conditions 

 affecting the nutrition of the cell, as scarcity of oxygen or presence of ether, the 

 mitotic cycle may be interrupted and replaced by amitotic division. The regular 

 mitotic process may be restored upon removal of the abnormal environment 

 (Nathansohn). 



Decidual cells showing amitotic division of 

 nucleus i^A-D) ; in ^ an attempt at mitosis has 

 occurred. X 410. 



nuclear and aberrant nuclear forms. 



