13.— Diagrams to illustrate the difference between the 

 old and the modern theory of chiasma-formation. 

 Maternal chromosome black, paternal one stippled (or 

 vice versa) a, an equal bivalent with a single chiasma 

 on the old theory ; b, the same on the new theory, 



c, the same bivalent on the old theory after rotation 



d, on the new theory after rotation, e and / provide 

 the proof that the new theory is the correct one. e is an 

 unequal bivalent with a single chiasma as actually found 

 /is what would happen in such a bivalent if the old 

 theory were true (never found). 



