332 T. H. BAST 



of the di^'iding nuclei have a horseshoe-shaped nucleus. ^lany 

 of the cells which Nowikoff illustates and which he classifies as 

 cells of the first type really appear to belong to the horseshoe type. 

 Nowikoff studied sections of bone, and that may have led to a mis- 

 interpretation of the shape of the nucleus. For example, a 

 horseshoe-shaped nucleus when cut at right angles to the bars 

 of the horseshoe, near or at the berid, appears dumb-bell 

 shaped. Or, if it is cut at an angle of 45° with the bars of the 

 horseshoe, it will look like a slightly bent dumb-bell, as many 

 of his illustrations show. Thus the many different forms depend 

 on the plane of section. In cartilage he found so many different 

 forms representing all stages between the first and second type 

 that he concluded that no two distinct types existed. 



This question, however, deserves a little further consideration. 

 The dumb-bell and horseshoe types in bone are too distinct and 

 constant to pass unnoticed. This distinction becomes all the 

 more apparent when we note that the shape of the nucleus is 

 definitely related to the position of the centrosomes. 



In the literature on amitosis very httle is said regarding the 

 centrosome. ]\Iany believe that it is entirely absent in cells 

 that divide by amitosis. Among them are Henneguy, Lenhos- 

 sek, Zimmerman, Heidenhain, Fuchs, Joseph, and Jordan in 

 ciliated cells, and others. Among those who have observed 

 centrosomes in amitotically dividing cells are Meyes, Studnicka, 

 Fischel, Eismond, Henry, Benda, Gurwitsch, Ach, Wallengren, 

 Ikeda, Erhard, Maximow, Nowikoff, Saguchi, Jordan, and others. 



The above list indicates that the centrosomes have been quite 

 generally .found in amitotically dividing cells. Whether these 

 centrosomes are of any functional importance in amitosis is a 

 question which is usually negatively regarded. Flemming and 

 ]\Iaximow always find the centrosome close to the nuclear 

 membrane and at the place where the constriction takes place. 

 In his 1910 paper Nowikoff tries to support Maximow's view 

 regarding the centrosomes. However, in figure 45 of his 1908 

 article he shows two centrosomes which lie one at each of the 

 two enlarged ends of the dumb-bell-shaped nucleus. In that 

 case the centrosomes certainly have moved apart just as they do 



