Th £ Nuclear C 



Y C L £ 



Sf>L/T 



M. 



A. 



O oil in q 



L 



P. 



Split 



4Xt«- 



D. 



M. 



MITOSIS 



ElOSIS 



Fig. 136. — Diagram to show the history of spiral forms in the nuclear 

 cycle, mitosis and meiosis, in relation to the division, repre- 

 sented by double lines in the side columns, and crossing-over 

 of chromosomes, represented by chiasmata, Xta. With normal 

 prophase the chromosomes divide during the resting stage, 

 with the precocious prophase, at the end of pachytene. 

 T, telophase ; Pj to P4, prophase ; M, metaphase ; A, anaphase ; 

 L, leptotene ; Z, zygotene ; P, pachytene ; D, diakinesis. 

 (R) and (L), directions of individual and relational coiling of 

 chromatids at mitosis and chromosomes at meiosis, numbered 

 according to the seven categories of Fig. 135. A circle repre- 

 sents the centromere, which divides at the end of metaphase in 

 mitosis and at the second division in meiosis. 



