AMITOSIS IN BONE CELLS 329 



Besides the views expressed above there are those who claim 

 that amitosis as observed in the above cases is not amitosis at 

 all. They would call it pseudo-amitosis or simply a peculiar 

 type of mitosis. We shall mention only a few of those who so 

 discredit amitosis: 



Hacker ('00). In eggs of cyclops. 



His ('00). In roots of Listera and Orchis. 



Hargitt ('06). In clava leptostyla. 



Richards ('09). In oogenesis of Taenia. 



Harman, Mary T. ('13). In sex-cells of Taenia teniaeformis. 



Conklin ('17). 



DISCUSSION 



The present observations on bone cells throw no further light on 

 theories 3 and 8, while theories 1, 5, and 6 are negatively answered. 

 The first part of theory 1, however, must receive some attention. 

 Bone cells are highly specialized cells, and it is probable that this 

 specialization does influence amitosis. That these cells have 

 entered a stage of degeneration is not supported by these studies. 

 Macewen believes that bone cells may at any time give rise to 

 osteoblasts, thus attributing to them a generative or regenera- 

 tive importance. 



Theory 6, which states that amitosis is a mechanical pinching 

 in two of the cells due to external pressure, was formulated by 

 Nowikoff as a result of his observations on amitosis in cartilage, 

 tendon, and bone. His two pictures of bone cells in his 1910 

 article on "Zur Frage nach der Bedeutung der Amitose" indeed 

 appear to support his view. In my own preparations no such 

 pictures were found. The only examples from which such a 

 view could be forced are shown in figures 2, 3, and 4. In figures 

 2 and 3 there is only a slight rarefication of cytoplasm, while the 

 nucleus is distinctly constricted but without signs of external 

 constriction. In figure 4 the cytoplasm is constricted, but the 

 nucleus is completely divided into two daughter nuclei. These 

 observations give the impression that cytoplasmic constriction 

 occurs as a normal process following nuclear division. In divid- 

 ing cells in which the horseshoe-shaped nucleus occurs — which 



