102 
THE ORGANIC CELL 
of each chromosome into two exactly equal parts, and the 
Diagram showing the Prophases of Mitosis. 
A. Resting cell with reticular nucleus and true nucleolus ; at C the 
attraction sphere containing 2 centrosomes. B. Early prophase, the chromatin 
forming a continuous spireme, nucleolus still present, above the amphiaster a. 
C, D. Two different types of later prophases. C. Disappearance of the primary 
spindle, divergence of the centrosomes to opposite poles of the nucleus (examples, 
some plant-cells, cleavage stages of many eggs). D. Persistence of the primary 
spindle (to form in some cases the ‘ central spindle ’) fading of the nuclear 
membrane, ingrowth of the astral rays, segmentation of the spireme thread 
to form the chromosomes (examples, epidermal cells of Salamander, formation 
of the polar bodies). E. Later prophase of type C ; fading of the nuclear 
membrane at the poles, formation of a new spindle inside the nucleus ; pre- 
cocious splitting of the chromosomes (the latter not characteristic of this 
type alone). F. The mitotic figure established; e.p. the equatorial plate of 
chromosomes. 
moving apart of the halves. This splitting of the chromosomes 
is of the greatest theoretical significance, for by it the original 
