THE CELL 



55 



centrosome to the chromosomes (Fig. 9, C). The two centrosomes 

 with their fibres constitute the amphiaster. 



2. During or immediately following the formation of the amphi- 

 aster, important changes take place in the nucleus. It increases in 

 size and loses the reticular appearance of the resting nucleus, its 

 chromatic elements becoming arranged in a long spireme-thread or in 

 several shorter threads, the closed skein or closed spireme. This next 



.1 



B 



Fig. 9. — Diagrams of Successive Phases of Mitosis. 



A, Resting cell, with reticular nucleus and true nucleolus; c, attraction sphere with 

 two centrosomes. 



B, Early prophase. Chromatin forming continuous thread — the spireme; nucleolus 

 still present; a, amphiaster; the two centrosomes connected by fibrils of achromatic 

 spindle. 



C, Later prophase. Segmentation of spireme to form the chromosomes; achromatic 

 Spindle connecting centrosomes; polar rays; mantle fibres; fading of nuclear membrane. 



D, End of prophase. Monaster — mitotic figure complete; ep, chromosomes ar- 

 ranged around equator of nucleus; fibrils of achromatic spindle connecting centrosomes; 

 mantle fibres passing from centrosomes to chromosomes. (E. B. Wilson, "The Cell," 

 The Macmillan Co.) 



becomes thicker and more loosely arranged, thus forming the open 

 spireme. That some chemical as well as morphological change has 

 taken place in the transformation of the reticulum of the resting 

 nucleus into the spireme is shown by the marked increase in staining 

 intensity, the spireme taking a much darker stain than the reticulum. 



