CKOSSING OVER AND CHROMOSOMES 109 



In the second division of this chromosome the longer 

 thread separates from the shorter one — the second is 

 therefore reductional. It is evident, especially from this 



d 



e 



f 



£ 



h 



d 



e 



f 



g 



h 



a 



d 



a 



Fig. 48. — A pair of chromosomes "B" in conjugation, 1; the same pair in conjuga- 

 tion in another individual in which one chromosome is shorter than the other, 2; same 

 in a third individual, 3; later stage showing chiasma of threads, 4. (After Wenrich.) 



last example, that the crossing of the threads is not an 

 indication that the division of the chromosome is neces- 

 sarily different from what it is when there is no sucli 

 crossing. What is more important is that the crossed 



