MEIOTIC PHASE IN MARSUPIALS 193 



Figs. 27 and 28 show that, (1) the chromomeres in a single 

 chromosome differ greatly in size, (2) the series of chromomeres 

 in a pair of conjugating chromosomes closely corresponds, 

 (3) conjugation takes place between the corresponding (homo- 

 logous) chromomeres. It will be noticed also that the final 

 union of chromomeres appears to be very intimate, all external 

 trace of duplicity having disappeared in the most completely 

 fused pairs. 



Syndesis is followed by the usual pachytene stage (PI, 14, 

 figs. 29-38), during the early part of which two compact bodies, 

 presumably X and Y, are conspicuous (PI. 14, fig. 31). These 

 soon unite into a single body, one or both of them often being 

 pulled out into irregular shapes during the process (PI. 14, 

 fig. 32). The autosomes remain filamentar and suffer a tem- 

 porary diminution of staining capacity. An important feature 

 which is very conspicuous in Heidenhain preparations subjected 

 to the right amount of extraction is that the stain is retained 

 much more tenaciously by certain of the chromomeres than 

 b}' others (PI. 14, fig. 32). The general significance of chromo- 

 meres is discussed below. 



As the chromosomes regain their staining powers towards 

 the end of the pachytene stage, the chromomeres again become 

 very conspicuous (PI. 14, fig. 33), as they are also in the diplotene 

 nucleus (PI. 14, figs. 34, 35). It is interesting to compare the 

 chromosomes shown in detail in fig. 35 with those in fig. 28, 

 the latter representing the conjugation of the chromosomes, 

 the former their separation. The correspondence between the 

 chromomeres of homologous chromosomes is still evident in 

 the diplotene stage, but now they are beginning to run together 

 on the contracting chromosome, ultimately to give rise to the 

 smooth chromosomes shown in fig. 36. 



I have not been able to trace with certainty the movements 

 of the sex chromosomes in the first meiotic division. In 

 regard to the second division, all that can be said is that the 

 number is clearly about ten or eleven, showing that there is 

 no second numerical reduction. 



The dimorphism of the secondary spermatocytes is not so 



