CYTOLOGy 



6-20 



the inner wall of the nuclear membrane. They are extraordinarily 

 long in the living state, reaching across the entire vacuole and bend- 

 ing to conform to the inner aspect of the opposite side of the mem- 

 brane. When the twelve long chromosomes are waving about in the 

 nuclear sap, the vacuole is completely filled with vibrating chromo- 

 some threads. In most killed cells the chromosomes are rather 

 short rods, which still retain their equidistant disposition around 

 the inner aspect of the nuclear membrane, but remain pointing in- 

 wards. Occasionally several of the chromosomes are polarized 

 towards the centrosome, but usually they are equidistantly distri- 

 buted around the entire surface. This disposition of the chromo- 

 somes means that their ends are in close proximity either to the 

 mitochondria or the ribose nucleoprotein dispersed from them. 



Fig. 6-14 Reconstruction of the Cell Shown in Fig. 6-13, c and d. 



As mitosis begins, the homologous chromosomes approach each 

 other but retain their attachment to the inner wall of the nuclear 

 membrane (fig. 6-20), so that they are found in pairs with the dis- 

 tal ends waving around in the nuclear sap. Preliminary to mitosis 

 the paired chromosomes shorten down to small cylindrical rods 

 less than one-tenth their original length, presumably by the normal 



