2 4 



HISTOLOGY 



certain of the chromatin rods or all of them represent one or more chro- 

 mosomes fused. These compound chromosome rods, when formed of 

 two chromosomes, are said to be bivalent; where more than two chro- 

 mosomes enter into their formation, they are said to be plurivalent. 



The chromosomes formed from the segmenting of the spireme as- 

 semble in a plane, through which the cell will divide, forming what is 

 termed the equatorial plate. In cases where the chromosomes are rod- 

 shaped they usually become bent into V-shaped bodies. The apices 

 of the bent chromosomes often converge so that the equatorial plate, 

 when seen from above or below, presents a radiating figure 1 (D). In 

 this position each of the mother chromosomes divide by splitting longi- 



D 





FIG. 20. A-I. Diagrams of chromatin changes during the division of a cell. 



tudinally into two daughter chromosomes. Two groups of daughter 

 chromosomes are thus formed (). One group is assembled above the 

 plane of cytoplasmic division, the other below at right angles to it (F). 

 Thus two groups of an equal number of chromosomes are brought to lie 

 opposite each other with the plane of approaching cell division lying 

 between them (G). The chromosomes of each group blend with one 

 another to form a spireme. About each spireme a nuclear membrane 

 . forms, and we have the dispireme phase of the chromatin (H}. The 

 spiremes next become more slender and finally break up into chromatin 

 particles to be distributed throughout the nuclear space (/). 



As a result of this series of chromatin changes there are two groups of 



1 This is frequently spoken of as the monaster. The word aster, however, is given to 

 another part of the mitotic figure ; so for clearness of terms we do not here use the word 

 aster for any figure formed by the chromatin. 



