88 . ETHEL NICHOLSON BROWNE 



is usually broken at this stage into two half rings, each one corre- 

 sponding to one of the original rods; and each half ring is clearly 

 longitudinally split. The two bars of each half ring frequently 

 intertwine, thus making a quite remarkable figure (fig. 92 A). 

 There seems to be no fusion at the points of crossing and no con- 

 nection of the elements of the two half rings inter se, so that the 

 figure lends no support to Janssens' ('09) chiasmatype theory. 

 After the stage of maximal expansion, a process of condensation 

 sets ill during which the enclosed space becorAes smaller and the 

 bars thicker; the first stage of the process is shown in figure 93 A-F. 

 The second longitudinal split has become so pronounced that it 

 entirely separates each half ring into two distinct elements. The 

 quadripartite nature of the ring is especially noticeable at the 

 juncture of the two half rings, for here the longitudinal bars 

 diverge considerably. In the very late prophase, the M-chromo- 

 some appears as shown in figure 94 A-D; the space enclosed in 

 the ring has become very much reduced, and the second longitudi- 

 nal split is still in evidence. The chromosome becomes arranged 

 on the spindle with its first longitudinal split in the plane of the 

 equator and its second longitudinal split in the plane of the spindle 

 axis. In a side view of the chromosome on a metaphase spindle, 

 therefore, the second longitudinal split is not visible, since it 

 hes in the plane of the paper (fig. 95 A, also figs. 29 C, 30 C, 31 C, 

 33 C, 34: A). If however one obtains an end view of the chromo- 

 some as it lies on the periphery of the spindle, i.e., so that the 

 place of union of the four elements is in the fine of vision, the 

 second longitudinal split is clearly seen at right angles to the 

 first (fig. 95 B). Also, in polar \dew of a metaphase plate, the 

 second longitudinal split is so clearly marked, that the ilf -chro- 

 mosome seems to consist of two distinct parts (fig. 95 C; also 

 figs. 25-28, 32). The first division plane passes through the 

 first longitudinal split. The second longitudinal split remains 

 during the anaphase; figure 96 A is a view of the chromosome 

 cut obliquely so that one of the components is at a higher level 

 than the other; figure 96 B shows the compound chromosome 

 Ma in end view. Figure 97 is a late anaphase showing the bi- 

 partite nature of the If-chromosome. This is also evident in 



