622 MURIKL ROIIKKTSON AND E. A. MIXCHIN. 



often very difficult to make out. It is best preserved in the 

 osmic-picrocarmine preparations ; after Hermann's fluid it 

 appears collapsed and shrunk or frayed out. A short way 

 above its origin the collar usually shows a distinct thickening, 

 visible as a horizontal hoop-like structure, especially when 

 tlie collar is a little contracted ; when it is expanded to its 

 fullest extent the lioop is difficult to make out as a horizontal 

 line, but its presence is marked by the fact that all the part 

 of the collar below it stands out stiff and firm, and is not 

 creased and folded like the part above. It is evident from 

 the appearances seen both in the i-esting and the dividing 

 cell that the collar for about 2 /x from its origin is thickened 

 and strengthened as compared with its distal portion. 



The nucleus of the collar-cell is about 5 /i in diameter and 

 more or less spherical in form, sometimes slightl}' flattened in 

 the vertical direction. The most conspicuous element in its 

 structural composition is a large grain, which stains deeply 

 with iron-h{i3inatox3'lin, and appears to be of the nature of a 

 karyosome. This structure is always present, and sometimes 

 double (figs. 1 c, 3, 7). The karysome is sometimes lodged 

 in a clear space (fig. 30, d, e,f) ; its position in the nucleus 

 varies. The remainder of the nuclear contents appear granular, 

 but in thin sections of the nucleus a fine network can be made 

 out (tigs, 30, e, /, r/), in the nodes of which the granules of 

 chromatin are lodged. These granules vary very much in 

 different nuclei in the same preparation, being sometimes so 

 fine as to be scarcely visible individually, while in other 

 nuclei they are coarse and irregular in size and shape (figs. 

 30 and 30, a, b, c). All transitions can be found between the 

 finely and the coarsely granular condition, but the two 

 extremes form two • well-marked types, which may be 

 characterised as the light and the dark type respectively. 

 It is worthy of note that nuclei of cells about to divide are 

 always of the light type, as will be pointed out in the next 

 section. 



The above description of the nuclei refers to preparations 

 stained with iron-hasmatoxj'liu. In material preserved and 



