132 THEORY OF EVOLUTION 



chromosome comes to be now on one side and 

 now on the other side of its mate. 



When the chromosomes sej)arate at the next 

 division of the germ cell the part on one side 

 passes to one pole, the part on the other to the 



85555^8288 



ooocP 



Fig. 64. Scheme to illustrate a method of crossing o%^er of 

 the chromosomes. 



opposite pole, (figs. 64 and 65). Whenever 

 the chromosomes do not untwist at this time 

 there must result an interchange of j^ieces 

 where they were crossed over each other. 



Janssens has found at the time of separation 



