10. Disjunction studies on interchanges have shown that sister spindle fiber regions do not separate in I, that crossing-over between the spindle fiber and the break is followed by disjunction of homologous spindle fiber regions, that the passage of two homologous spindle fiber regions to the same pole in I is increased when the crossing-over is decreased, and that whether 4 or 6 types of spores will be formed and their proportions depend upon the relative distances between the spindle fiber regions and the breaks coupled with crossing-over in these regions.