62 THE CHROMOSOMES 



reason why they separate after splitting is probably 

 merely that the two paternal threads are farther away 

 from the two maternal ones than they are from one 

 another. 



DiAKINESIS 



This- stage corresponds to the late prophase of an 

 ordinary mitotic division. Diplotene passes quite 

 gradually into diakinesis so that it is quite impossible 

 to say when one ends and the other begins. There 

 is much to be said for abolishing the term diakinesis 

 altogether and substituting ' late diplotene ' for it. 

 The most noticeable difference between the bivalents 

 in diakinesis and diplotene is that they have become 

 much thicker and shorter in diakinesis. As a result 

 of the thickening of the chromatids the split between 

 them becomes more difficult to see — in many cases it 

 becomes quite invisible by the end of diakinesis (it 

 will be remembered that a similar phenomenon takes 

 place at mitosis). ' Rotation ' is usually completed 

 by the beginning of diakinesis but ' terminalization ' 

 may continue right up to the metaphase of the first 

 meiotic division. 



As in the late prophase of mitosis there is in dia- 

 kinesis a strong tendency for the thickened chromo- 

 somes to move to the periphery of the nucleus and 

 to arrange themselves on the inside of the nuclear 

 membrane (yet another result of the general surface 

 repulsion force). 



Prometaphase 



As in the case of mitosis we call the period between 

 the disappearance of the nuclear membrane and the 

 moment when the spindle is fully formed, prometa- 

 phase. At this stage the diakinesis bivalents have 

 contracted still further and begi^i to be associated 

 with the developing spindle. It will be remembered 

 that at mitosis the contraction of the chromatids is 

 due to the actual substance of which they are com- 



