76 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
C. Tue INDIVIDUALITY OF THE CHROMOSOMES. 
a. The selected Chromosome Pairs. 
The method adopted in the study of the subject of synapsis — that 
of following the history of individual chromosome-pairs — has natu- 
rally led to a consideration of the subject of the individuality of the 
chromosomes, that is, their persistence as morphological entities 
through all the stages of nuclear activity. I have already attempted 
to demonstrate that each of the chromosomes of the last sperma- 
togonial division gives rise to a single leptotene thread and that these 
single threads conjugate two-by-two in the zygotene stage. It will 
be more convincing, however, if we can follow some particular chromo- 
some-pair through these difficult stages. 
1. Chromosome-pair A.— As the chief characteristic by which the 
chromosome-pair A could be recognized in the pachytene and later 
stages of the first spermatocytes, I have already described its great 
density and staining capacity. If there is a persistence of individual 
chromosomes from the spermatogonia to the spermatocytes, we should 
expect to find in the former a pair of chromosomes exhibiting th: same 
peculiarities that the pair did in the later generation. Such a pair 
can, indeed, be found in the telophases not only of the last spermato- 
gonial division but of the earlier spermatogonia as well. Figures 66 
and 67 (Plate 6) show such pairs of chromosomes more deeply stained 
than their fellows. Figure 66 shows one of the earlier generations of 
spermatogonia, as is indicated by the vesicular condition of the ac- 
cessory chromosome, and figure 67 represents a telophase of the last 
spermatogonial division, as is shown by the condensed accessory at 
this stage. 
It is difficult to follow all the changes that these chromosomes 
undergo in their transformation into pachytene threads, but I believe 
that most of the stages are represented in the series of drawings, 
figures 67-78. Figure 67 corresponds to a stage midway between 
those shown in figures 21 and 23 (Plate 2). Figure 68 is of a stage 
corresponding very closely to that in figure 25 (Plate 3). In figures 
68 and 25, two bands or “blocs” of chromatin can be seen which are 
more deeply stained than the other chromatin-blocs. The accessory 
chromosome is distinguishable by its characteristic density and its 
position at the periphery of the nucleus. The polar granules are also 
distinguishable. The chromatin in these darker blocs (A in both 
