THE CELL AND CELL DIVISION 45 



and so is separated by a considerable intervening vegetative 

 period from the other events of mitosis or the doubling of 

 other parts (Fig. 20, A). This vegetative phase of cell life is 

 frequently referred to as the "resting" period or interkinesis; 

 a state of inaction is not implied by the term " resting," for 

 during this period the cell is performing its normal and char- 

 acteristic functions as a tissue cell; the word merely indicates 

 that the cell is not undergoing any active phase of division. 

 The termination of the vegetative phase and the immediate 

 inauguration of mitosis is ordinarily first distinguishable in 

 the structure of the nucleus. The chromatin granules become 

 more distinct, enlarge rapidly, and undergo some change in 

 chemical constitution indicated by an increase in staining 

 capacity (Fig. 20, A; 22, A). As the chromatin increases some 

 of the granules or flakes come to be arranged in a linear, or 

 sometimes bilinear series, still upon some of the linin threads 

 which share in this arrangement. Thus the chromatin and 

 linin form a tangled thread or ribbon called the skein or spireme 

 (Figs. 20, B; 21, B; 22, B). 



We should note here that at this time the chromatin of the 

 nucleus which is not included in the spireme, often indeed the 

 greater part of the whole amount of this material, is thrown out 

 into the cytoplasm and dissolves (Fig. 32) ; the more fluid parts 

 of the nucleus are also thrown into the cytoplasm by the 

 dissolution of the nuclear membrane. It may thus be only a 

 comparatively small part of the whole nuclear structure that is 

 formed into the spireme proper. 



, The spireme may be quite continuous throughout the nucleus, 

 or it may appear from the first as a fragmented thread com- 

 posed of several short pieces; when in this latter condition it is 

 spoken of as a segmented spireme. In a few cases the spireme 

 stage is largely suppressed and the chromatin granules collect 

 immediately into compact groups without indication of a 

 skein stage. Tke_ljnin.jaetwQrk,in- part becomes a sort of fine 

 core throughout the spireme and in the extra-chromatic region 

 remains as a network of naked fibers. The latter portion soon 

 becomes polarized so that its fibers converge, more or less 



