MITOSIS AND AMITOSIS 



Prophase. i. The centrosome divides and the two minute bodies 

 resulting from the division move apart, ultimately occupying positions at 

 opposite poles of the nucleus (I-III). 



2. Astral rays appear in the cytoplasm about each centriole. They 

 radiate from it, and the threads of the central or achromatic spindle are 

 formed between the two 



asters, thus constituting 

 the amphiaster (II). 



3. The nuclear mem- 

 brane and nucleolus dis- 

 appear, the karyoplasm 

 and cytoplasm becoming 

 confluent. 



4. During the above 

 changes the chromatic net- 

 work of the resting nucleus 

 resolves itself into a skein, 

 or spireme, which soon 

 shortens and breaks up 

 into distinct, heavily-stain- 

 ing bodies, the chromosomes 

 (II, III). A definite num- 

 ber of chromosomes is 

 always found in the cells 

 of a given species. The 

 chromosomes may be 

 block-shaped, rod-shaped, 

 or bent in the form of a 

 Uor V. 



5. The chromosomes 

 arrange themselves in the 

 equatorial plane of the 

 central spindle (IV). If 

 U- or V-shaped, the angle 

 of each is directed toward 



center. The 



/\ 



A 



FIG. 8. Diagrams of the phases of mitosis (Schafer). 



a common 



amphiaster and the chromosomes together constitute a mitotic figure, and 



at the end of the prophase this is called a monaster. 



Metaphase. The longitudinal splitting of the chromosomes into ex- 

 actly similar halves constitutes the metaphase (IV, V) . The aim of mitosis 

 is thus accomplished, an accurate division of the chromatin between the 

 nuclei of the daughter cells. 



