502 D. H. WENRICH 



primary or secondary but let us assume that number 3 has the 

 chi'omatids separated along the primary plane, with the vesicle 

 attached to the chromatids of one conjugant. This tetrad is at 

 a stage early enough so that it could be expected to undergo 

 chromatid movements before it became condensed and oriented in 

 the metapase. If ring 3 has arisen from a separation along the 

 primary spht, then the free ends (no. 4) must have separated 

 along the secondary split. So, also, number 2; while number 1 

 would have separated along the primary split. Now the question 

 may be asked if there is any reason why the further separation of 

 chromatids should prevail along one plane rather than along the 

 other. Does not, for instance, the greater extent of the separa- 

 tion in ring 2 and the smaller size of ring 3 indicate that further 

 movement is likely to be in the plane of separation of rings 2 and 

 4 which we have assumed to be the secondary plane? Would 

 not such a process give us a condition similar to that in figure 10 

 with the long free arms at the right having opened out beyond 

 the apical point? Again, could not separation proceed to the 

 enlargement of ring 3 at the expense of 2 and 4 and give rise to 

 such a form as occurs in figure 14? 



Similar situations are presented in the series from Trimero- 

 tropis in figures 15 to 19. In figure 15, so far as can be ob- 

 served, there would be just as much chance of separation along 

 one plane as the other, since we cannot recognize the synaptic 

 point in this element. In figure 17, the middle ring might be- 

 come enlarged so as to produce a condition such as is shown in 

 figure 19, or the ends at the right might be separated and re- 

 fiexed toward the left as indicated in figure 18, as previously 

 mentioned (p. 488). In any case the primary cannot be differ- 

 entiated from the secondary plane of separation, and in many 

 ways it seems as reasonable to assume one as the other as likely 

 to prevail in anaphase. 



From the heteromorphic pairs another line of argument may 

 be developed. If we assume as established that the hetero- 

 morphic pairs in Trimerotropis always divide reductionally as 

 they appear to do, we have a basis upon which to argue that the 

 other atelomitic chromosomes should behave in the same man- 



