48 



GENERAL EMBRYOLOGY 



FIG. 21. Diagrams of the process of mitosis. From Wilson, "Cell," slightly 

 modified. A. Resting-cell with reticular nucleus and true nucleolus; at c the 

 attraction-sphere containing two centrosomes. B. Early prophase; the chroma- 

 tin forming a continuous spireme, nucleolus still present; above, the amphiaster 

 (a). C.D. Two different types of later prophases; C. Disappearance of the pri- 

 mary spindle, divergence of the centrosomes to opposite poles of the nucleus 

 (examples, many plant-cells, cleavage-stages of many eggs). D. Persistence of 

 the primary spindle (to form in some cases the "central spindle"), fading of the 



