346 
LESTER W. SHARP 
shown by the chromosomes as they form the reticulum during the telophase 
(compare figs, ii and 14). 
The separating portions of the reticulum, each of them representing 
a chromosome, continue to condense, and the anastomoses between them 
become further broken down, so that they soon stand out with great dis- 
tinctness (fig. 15). Since the early prophasic changes are in many respects 
simply the reverse of those occurring in the telophase, the structure of the 
chromosomes at these two stages is almost precisely the same. Vacuoles, 
or spaces enclosed during the condensation of the reticulum, may be found 
in all positions, median and peripheral, while large cavities open to the 
exterior on all sides. Transverse sections of chromosomes in this condition 
are shown in figure 16. It is perfectly evident that at this stage of the pro- 
phase, just as in the telophase, each chromosome is simply an irregular 
alveolar-reticulate cylinder, and has the form neither of a split thread or 
ribbon nor of a ladder-like structure characteristic of the incompletely 
split chromosomes of the later prophases. At the stage shown in figures 
15 and 16 the chromosomes are in no sense double; the split marking the 
line of separation at the next metaphase has not yet appeared. 
Each alveolar-reticulate chromosome now becomes transformed in a 
peculiar manner into a single (i.e., not double) slender thread. Of all the 
morphological changes undergone by the chromosomes during mitosis this 
is one of the most difficult to observe and interpret. The staining must 
be particularly sharp to bring it out properly, and it is probable that it is 
passed through with considerable rapidity. These facts account in part 
for the absence of these stages from the descriptions of mitosis given by 
many investigators, and consequently for misinterpretations of the telo- 
phasic and early prophasic changes with respect to the splitting of the 
chromosomes. The transformation process, which is in progress in the 
nucleus shown in figure 17, is as follows. 
As the chromatic material becomes increasingly condensed, the more 
slender strands, like the anastomoses at an earlier stage, and also the 
thinner walls bounding the peripherally situated enclosed spaces, become 
broken down, leaving the heavier portions of the chromosome in the form 
of a very irregular zigzag thread of uneven thickness. Various stages in 
this process are shown in figure 18. At the points marked a the dissolution 
of the finer portions can be seen occurring, and the reason for the crooked 
and lumpy appearance of the newly formed slender thread is apparent. 
In many cases the arrangement of the open spaces is such that the chromatic 
thread has a roughly spiral aspect, but in view of the relation it bears to 
the reticulate stages of the earlier prophases it can hardly be said to arise 
endogenously within the chromosome as some workers have maintained. 
The crooked thread at once begins to straighten out; this change in shape 
is associated with an equalization of the chromatic material, so that the 
thread gradually becomes more uniform in diameter. Here and there in the 
