104 BIOLOGY: GENERAL AND MEDICAL 



hand, they are viewed from a point at right angles to 

 the axis of the nuclear spindle, it will be found that they 

 all lie in a plane perpendicular to the axis of the spindle 

 known as the " equatorial plane." 



3. The Separation of the Chromosomes and the Forma- 

 tion of Daughter Stars. The chromosomes, which it will 

 be remembered have undergone a longitudinal cleavage, 

 now manifest a phenomenal change of position. Begin- 

 ning at the centre, each half moves from its fellow and 

 directs itself toward one end of the nuclear spindle until 

 there has been an exact division of the filaments, one- 

 half having gradually moved into the polar field, the 

 other half into the hypopolar field. 



This results in the formation of a double figure, the 

 amphiaster or " daughter stars." Each of these exactly 

 resembles the aster or mother star except that its size 

 is smaller. 



During this phase of the nuclear changes the cyto- 

 plasm shows an increasing constriction in the line of 

 the equatorial plane which progressively deepens so that 

 about the time that the nuclear changes are perfected 

 the separation into two cells is also completed. 



4. The Transformation of each Daughter Star into a 

 Perfect Nucleus. This is accomplished by a succession 

 of events corresponding to those described as charac- 

 terizing the phase during which the nucleus prepares 

 for division, except that they occur in the reverse order 

 i.e., the chromosomes abandon their star-like formation, 

 adjust themselves to form a spirem, become mixed with 

 the linin filaments, and lose their distinctness until the 

 usual nuclear appearances are resumed. 



This general outline of the cell division is, however, 

 subject to many modifications necessitated by the 

 simplicity and complexity of the cells and the number 

 into which they divide. 



In those cells in which no nuclei can be discovered by 

 existing methods of examination, no nuclear changes 

 can be associated with division. The cell having grown 



