RIarq uelte, Manifestations of polarity in planl cells which usw. 289 



closer together. These conditions are still more clearly skowii in 

 cells in which a more considerable Space remains between th<- 

 polar structures and the plasma membrane as Urequently happens 

 in cells which are elongated more tlian usual. In these cases the 

 cytoplasm next to the outer boundary of the polar structures 

 appears as a dense almost finely granulär mass, further outwards 

 towards the plasma membrane its structure becomes looser. Nol 

 rarely this denser part of the cytoplasm is fairly sharply bounded, 

 resting 011 the polar structure like a more or Less crescent 

 shaped mass. The Strands or lamellae of the less dense adjacenl 

 cytoplasm extend out from this denser mass to the cell periphery 

 in a more or less radial arrangement. The appearances jnst 

 described are especially well brought out in preparations stained 

 in iron-haematoxylin. The dense cytoplasmic mass stains more 

 intensely than the surrounding cytoplasm and strongly suggests 

 on archoplasmic region such as has been figured for various 

 animal cells. 1 ) 



When the polar structures have reached their definitive posi- 

 tions or even as they were moving away from the nucleus, the 

 spindle fibers begin to appear, and it is to be observed that withont 

 exception they extend between the polar structures and the adjacent 

 surface of the nucleus. In the earlier stages of spindle formation 

 the fibers present the appearance of a tangled network. Whether 

 the fibers actually brauch and anastomose or whether the appear- 

 ance is merely due to an intertwining of sinuous but unbranched 

 fibers may be left undecided for the present. While the spindle- 

 fibers are developing the nucleus changes its shape. It expands 

 laterally and at the same time shorteus in the direction of its form er 

 long axis so that finally its long axis is perpendicular to that of 

 the cell. The nucleus no longer has the smooth, regulär, ellipsoidal 

 outline it possessed in the earlier stages but shows a shallow inden- 

 tation at the places where the spindle fibers come in contact with 

 it. The appearance strongly suggests a pressing in of the nuclear 

 membrane on the part of the spindle fibers. Whether such is 

 actually the case I have not determined. 



Simultaneously with these changes in the shape of the nucleus 

 its membrane begins to disappear. The stages in the disappearance 

 of the membrane are not easily followed since the nuclear membrane 

 is never very conspicuous in these cells. However, to all appearances 

 it seems evident that the membrane first disappears at the points 

 where the spindle fibers come in contact with it. (Fig. 4) The 

 chromosomes at this time lie, more or less wound about each other. 

 fairly uniformly distributed through the nuclear space. 



The spindle fibers begin to stand out more sharply now. assume 

 a straighter course, and approach each other more closely at their 

 distal ends until finally an exceedingly sharp pointed spindle 



*) Hermann, F.: Beiträge zur Lehre von der Entstehung der karyo- 

 kinetischen Spindel. (Arch. f. mikr. Anat. Bd. XXXVII p. 569. See figs. ;5.5, 

 etc. PI. XXXI.) 



