20 THE HUMAN BODY. 



local accumulations of chromoplasm; a membrane (nuclear 

 membrane) which surrounds the nucleus of cells not in process 

 of division is also probably composed of chromoplasm. 



The first observed step in cell division is binary division of 

 the attraction-particle: its halves evolve a set of very fine 

 achromat in filaments uniting them, so that each half is one of 

 the poles of a spindle-shaped collection of fibres, the nuclear 

 spindle. Meanwhile the nucleolus and nuclear membrane 

 disappear, being probably taken up into the rest of the chro- 

 moplasm, which now, instead of its original reticular arrange- 



- d. b 



FIG. 0. Diagrams ot a nucleus in an early stage of karypkinesis, A showing the 

 polar, B the anripolar region; o, nuclear or achromatin spindle; />, part of general 

 cell-protoplasm around the nucleus; c, looped chromatic filament; d, nucleoplasm. 



ment, takes the form of a single long chromatic filament 

 coiled in the nucleoplasm. At one portion of the nucleus 

 (pole) the loops of the chromatic filament leave a space free 

 from them (Fig. 9, ^4), and in the neighborhood of this space 

 the nuclear spindle is first seen within the nucleus. At the 

 opposite side of the nucleus or antipole (Fig. 9, B) the loops 

 of the chromatic filament leave no clear space, but cross ir- 

 regularly. In the next stage the loops at the antipolar end 

 break through, and in this way the filament is divided into a 

 number of irregular elongated Vs, each with its closed angle 

 near the pole and its open end near the antipole. The spindle 

 meanwhile passes to the centre of the nucleus and takes a posi- 

 tion in which its long axis coincides with that joining pole and 

 antipole, and then the Vs of chromoplasm become shorter and 

 their limbs thicker, and they also shift position so as to group 

 themselves radially around the equator of the spindle (A, Fig. 

 10) with their angles directed centrally. Each V then di- 

 vides along its whole length, and one half passes towards the 



