Ii6 MEIOSIS IN DIPLOIDS AND POLYPLOIDS 



Careful comparison of several such cases shows that the centro- 

 meres of the two " separating " chromosomes are no further apart 

 than those of the larger chromosomes, but the parts of the chromo- 



FiG. 36. — Diagram showing chromatid behaviour in anaphase 

 separation of bivalents of different types. A. Single chiasma : 

 one chromatid in each daughter chromosome shows a constric- 

 tion. This constriction is momentary and has been best seen in 

 living material (Belar, 1928, Fig. 266 ; cf. Janssens, 1924, 

 Fig. 259 ; Belling, 1926 b, Fig. 6). 



B and C. Two comparate chiasmata : the chromatids 

 are associated distally to the second as they were proximally to 

 the first (E. R. Sansome, 1932 ; cf. Janssens, 1924, Fig. 259 ; 

 Belling, 1926 b, Fig. 6 ; Newton and D., 1930). The point at 

 which the chromatids separate last appears to show a connection 

 (D., 1929 b, Figs. 29 a and 56). 



C. The loops formed by the two pairs of chromatids interlock 

 (Janssens, 1924, Fig. 259). One loop then breaks its terminal 

 association in separating (Belar, 1929 a, Fig. 9). 



D. Two disparate chiasmata : the anaphase figures 

 are asymmetrical in consequence (Janssens, 1924, Fig. 259 ; 

 Newton and D., 1930). 



N.B. — Cf. also Saicamura, 1915 ; Maeda, 1930, a and b ; 

 Richardson, 1936, D., 1936 d. 



somes between the centromeres and the terminal chiasma are so small 

 as to be drawn into a fine thread which may be invisible (Chorthippus, 

 D., 1936 d, and Fig. 49 c). 



