THE MECHANISM OF HEREDITY 35 



One member of each pair of chromosomes comes from 

 the father, its mate from the mother. If, when the con- 

 jugants come to lie on the spindle, all the paternally de- 

 rived chromosomes were to go to one pole, and all the 

 maternally derived to the other pole, the two resulting 



\/ \/ 



x * 



f *l 



■ op i 



I I 



/ \ ' / \ 



. 



Fig. 23. 

 Diagram to illustrate the random assortment of a pair of chromo- 

 somes with respect to the X-chromosome. (After Carothers.) 



germ-cells would be like those of the father and of the 

 mother. There is no a priori reason for supposing that 

 the conjugants would behave in this way, but it has been 

 extremely difficult to prove that they do not do so, because 

 from the very nature of the case, the conjugating chro- 

 mosomes being alike in shape and size, it is not as a rule 

 possible to tell from observation which member is pater- 

 nal, which maternal. 



In recent years, however, a few cases have been found 

 in grasshoppers where slight differences are sometimes 



