188 DIVISIONS INDUCED IN LYMPHOCYTES 



large number of chromatin granules (figs. 41-2) are 

 found which really are in the clear cytoplasm, and 

 they are frequently extruded with the cytoplasm into 

 the pseudopodia, especially if amoeboid movements are 

 excited by atropine. When a lymphocyte "flagellates," 

 these granules are thrust out through the cell-wall 

 and become separated. When the cells are on jelly 

 which makes them divide, amceboid movements cease, 

 and then the procedure is as follows: The nucleolus, 

 which is shaped like a minute ring, and stains as if 

 it was composed of chromatin, splits either into two 

 rings 1 (figs. 43-4), or into two dots of chromatin 

 which form the centrosomes. They then separate 

 and emerge at opposite poles of the cell out through 

 the mass of granules in the cytoplasm (figs. 457), 

 and in doing this they seem to pull out the nucleus 

 into the form of a spindle. The chromatin granules 

 of the cytoplasm in the meantime are gradually 

 collected into masses round the waist of the spindle 

 (fig. 44), and ultimately they form a belt of 

 chromatin round it on its outside (figs. 48-9). In 

 a specimen in which one can see down through the 

 spindle it will be observed that this belt divides into 

 a number of chromosomes (figs. 50-1), which become 

 semilunar-shaped with their points inwards (figs. 52-5). 

 Each chromosome is in contact with its neighbours 

 at its points (figs. 62-3). Each one of them then 

 divides into two (fig. 64). One half of every chro- 

 mosome travels towards one nucleolus-centrosome, 



J One of us (J. W. C.) has recently seen a ring-shaped centrosome in the 

 act of division. It appeared hour-glass shaped. 



