Interkinesis 



This is the interphase stage between the two divisions. It may be of 

 relatively long duration, in which case a cell wall is usually laid down 

 between the two nuclei to give a two-celled or dyad stage. On the other 

 hand it may be of such short duration as to be practically nonexistent. 

 In this case a cell wall is seldom laid down and the chromosomes go 

 through the second division relatively unchanged morphologically. In 

 animals the two cells of the dyad are normally separated except for a thin 

 cytoplasmic connection. 



Second Division 



Prophase II 



If there is no interkinesis, this stage is eliminated. In any event it 

 appears to be rapid, but like any prophase, is essentially a stage of con- 

 traction and coihng. 



Metaphase II 



The kinetochores which have been holding the two chromatids to- 

 gether line up as at somatic metaphase, and divide. 



Anaphase II 



Sister kinetochores separate to the poles, pulling with them the chro- 

 matids to which they are attached. 



Telophase II 



This stage involves the reconstitution of interphase nuclei and the 

 laying down of cell walls to give four cells, known as a tetrad in plants. 

 In animals there are four separate cells in the male. In the female, a 

 microcyte called the polar body is usually budded oflf after the first 

 division and a second polar body after the second division so that the 

 end product of meiosis is a "reduced" egg and two or three polar bodies. 

 Thus the final result of these two divisions is four cells, each with a 

 complete chromosome set and half the somatic number of chromosomes. 



In animals the end products of meiosis become gametes, while in 

 higher plants a number of purely somatic-type divisions occur to give the 

 gametophytic generation, which is haploid. 



As in mitosis, this description should be considered a norm. Varia- 

 tions occur both as accidents and as established processes. For example, 

 chiasma formation appears to be absent in meiosis of the males of 

 certain insects. 



130 / CHAPTER 5 



