The Microscope. 229 



in it. From the avidity with which these granules take up stains 

 the substance composing them has been called " Chromatin." 

 In many resting nuclei the Chromatin seems to be almost en- 

 tirely wanting, but as the nucleus prepares to divide, it becomes 

 very abundant, as is shown by the deep coloring of the nucleus 

 at this time. 



Besides the nuclear filaments, there are usually to be found 

 one or more nucleoli, rounded bodies that are often very con- 

 spicuous. These usually stain deeply, but occasionally this is not 

 the case. 



The first indication of approaching division in the nucleus is 

 usually an increase in volume, followed shortly by a shortening 

 and thickening of the nuclear filaments which become much 

 more distinct, and owing to the increased amount of Chromatin 

 in them, color much more deeply than in the resting nucleus. 

 As the preparations for division proceed, the filaments continue 

 to shorten and the Chromatin increases in quantity, the separate 

 granules often coalescing until the filaments appear as short thick 

 loops stained almost uniformily, and very vividly. By this time 

 the nucleolus has usually disappeared and it is still a question 

 •what becomes of it. 



Presently the nuclear membrane disappears entirely and the 

 nuclear filaments, which have separated more and more, lie free 

 in the centre of the cell. They quickly arrange themselves in 

 the form of a flat disk (nuclear-plate) across the centre of the 

 cell, in the plane of the future division wall (Fig. 10), and now 

 we may see, with care, delicate lines in the protoplasm which 

 Tun from the disk and converge at the poles of the cell, forming 

 a spindle-shaped figure with the nuclear-plate at the equator. 

 This stage is called the "nuclear-spindle," and probably the 

 number of spindle-fibres corresponds to the number of the seg- 

 ments in the nuclear-plate. (Fig. 10). 



About the time that the nuclear plate is complete, the seg- 

 ments, which commonly are V-shaped, divide longitudinally 

 into two equal parts, and as these separate, the points of the two 

 new segments are divided toward opposite poles of the spindle, 

 the angles remaining for a short time in contact. 



Now begins the separation of the two sets of segments which 

 travel along the spindle-fibres towards the poles. As they sep- 

 arate, numerous very fine threads connecting them become visi- 



