26 THE CHROMOSOMES 



set. The actual longitudinal division of the chromo- 

 somes takes place during the resting stage when they 

 are invisible (or at any rate un-fixable), but the split 

 halves (chromatids) remain closely approximated, 

 due to the existence of a force of attraction between 

 them, up to the beginning of anaphase. The forma- 

 tion of the spindle and the behaviour of the chromo- 

 somes at metaphase and anaphase depend on a 

 special part of each chromosome, the spindle attach- 

 ment, which persists throughout the mitotic cycle 

 and is a self-perpetuating cell-organ with peculiar 

 properties. 



