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T. H. BAST 



This type is well represented in bone cells by figures 5 to 12. 

 Jordan describes this type in the blood and the bone-marrow of 

 the frog and in the bone-marrow of the rabbit. Flemming's 

 figure 5 is of this type. Most of Nowikoff's and Maximow's 

 figures look as though they belonged to this type. Thus Maxi- 

 mow's figure 9 shows a nucleus which looks dumb-bell-like in 

 shape. A comparison of this nucleus with the middle nucleus of 

 my figure 10, which is a horseshoe-shaped nucleus viewed from 

 one end, makes the similarity very apparent. Some of Arnold's 



a b c a 



Text fig. 1 Diagrammatic sketches representing the four types of amitotic 

 nuclear division, a, Type 1. The nucleus is dumbbell-shaped with the centro- 

 somes at the poles of the dividing nucleus, b, Type 2. The nucleus is horseshoe- 

 shaped with the centrosomes within the bend of the nucleus, c, Type 3. A plate 

 like structure marks the plane of division of the oval-shaped nucleus. Centro- 

 somes are near the surface of the cells, but they may be found in other positions 

 or may be entirely absent, d, Cell fragmentation. The mass of protoplasm on 

 top contains a small amount of unorganized nucleoplasm. The mass at the bot- 

 tom contains no nuclear material. 



observations belong here. Heidenhain has given the most 

 extended list of descriptions and illustrations of this type. 



Type III. In this type the centrosome is f unctionless ; it 

 neither moves apart nor exerts any influence on the nucleus. 

 In some cases the centrosomes may be absent. In the earl}^ 

 stages of division a plate-like structure marks the plane of 

 cleavage (text fig. 1, c). A narrow notch on one surface of the 

 nucleus often initiates separation of the daughter nuclei. The 

 ciliated cells illustrated by Jordan and Saguhci and the fat cell 

 by Nakahara belong to this type. I have found many nuclei 



