AMITOSIS IN BONE CELLS 333 



in case of mitosis. Saguchi presents a similar moving apart of 

 the centrosomes in his figure 49, plate 3. In this case the nucleus 

 has not moved apart as far as the one shown by Nowikoff or 

 the one in my figure 2. This incomplete polar movement of 

 the centrosomes accounts for the shape of the nucleus. 



In my observations on bone cells a definite relationship between 

 position of the centrosomes and the shape of the nucleus could be 

 established. In trying to correlate this observation with those 

 of other observers and with the various theories on amitosis, 

 it appeared that amitotic nuclear forms can be classified accord- 

 ing to the functioning ability of the centrosomes. If it is true, 

 as many believe, that a cell may divide amitotically and then 

 return to the mitotic type of division, and if the centrosome is 

 active in mitosis and inactive in amitosis, then it is not strange 

 that intermediate stages of centrosomal activity should occur. 

 Food conditions, specialization, or external stimuli may disturb 

 the equilibrium of the nuclear chromatin while the centrosome 

 remains functional, thus causing amitotic division, or these 

 disturbing factors may impair the migrating power of the centro- 

 somes; or finally they may paralyze the entire mechanism which 

 is active in mitosis and thus cause amitotic division. 



In view of these observations and considerations, the following 

 classification of amitotic types seems warranted: 



Type I. The nucleus is dumb-bell shaped. The centrosomes 

 have moved apart and placed themselves one at each end of the 

 elongated nucleus and apparently 'exert a pull on it' (text fig. 1 a). 



The only difference between this tj^pe of amitosis and mitosis 

 is the inability of the nuclear chromatin to rearrange itself. 

 Examples of this type are shown in figures 2, 3, and 4. The 

 illustrations of Nowikoff and Saguchi referred to above belong 

 under this type. 



Type II. The nucleus is horseshoe shaped. The centrosomes 

 do not move apart, but they still 'exert a pull' on the nucleus. 

 In some cases the movement of the nucleus around the centro- 

 somes progresses to such an extent that the ends of the nucleus 

 meet, thus forming a ring around the centrosomes (text figure 

 1, +b). 



