ROBERTSON: CHROMOSOME STUDIES IV. 283 



mate (s) lie to one side of the nucleus coiled in corkscrew fashion, the 

 spiral turning toward the right. Both point to what is probably the 

 distal end of the cell. 



Figs. 9a, 96. No. 5x and s pairing in synapsis stages slightly later 

 than figure 8. 



Figs. 10a, 10b. Similar stages. Each accessory shows a longitudinal 

 split. 



Figs. 11«, lib, lie. Similar stages; all taken from one cyst. Acces- 

 sory chromosomes usually lie near together, but may lie on opposite 

 sides of the nucleus. Inequality of the two is apparent. 



Figs. 12, 13. Fine spireme stages following the bouquet stage. The 

 accessory and its supernumerary mate may lie close together or on oppo- 

 site sides of the nucleus. Both always lie on the nuclear membrane. 



Figs. 14a and 146. Cell from two sections. Early prophase. Six 

 pairs of autosomes form tetrads. The normal 5x accessory and its mate 

 near by. Note shortness of the supernumerary. Both are split. 



Figs. 15o, 156, 15c. Three similar stages from other cells of the cyst. 

 Both chromosomes split. 



Fig. 16. Similar stage; complete cell. Chromosome No. 6 moved out- 

 ward. 



Figs. 17 to 21. Division of first spermatocyte. Supernumerary going 

 either with the accessory or to the opposite pole. In 65 to 75 per cent of 

 the cases it lay near the accessory, but might not (figs. 20, 21). All other 

 chromosomes of normal size and dividing normally. Chromosome No. 5 

 slightly displaced to right in figure 17. 



Figs. 22 to 25. Second spermatocyte division, polar view, showing six 

 seven and eight chromosomes, depending upon whether No. 5x and s were 

 absent or present, either one at a time or both. 



Figs. 26, 27. Second spermatocyte division, lateral views of the spindle, 

 showing that all chromosomes divide. Six chromosomes in one, the 5x 

 and the s chromosome absent; eight in the other, both the 5x and the s 

 chromosome present. 



