74 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
erably greater than in the stage last described. The anastomosis is 
to be seen more particularly at the sides of figure 25. Through the 
middle of this figure the individual spiral threads seem to be more 
easily distinguishable, and I am inclined to believe that the two which 
stain more deeply than the others are the members of the A pair of 
chromosomes. The stages including and following this reticular 
stage are hard to represent in a drawing of the kind employed, owing 
to the difficulty of portraying in their natural relations the parts seen 
at different planes of focus. Careful study has always convinced me, 
however, that the uncoiling and elongating threads are single, con- 
tinuous, and not united into an indiscriminate network. I have 
selected in figures 26 and 27 views favorable for drawing where some 
of the threads, at least, are definitely separate and continuous across 
the diameter of the nucleus. 
At the stage represented in figure 28 (Plate 3) the unwinding of the 
coiled threads has been completed, but the threads have as yet no 
definite orientation. At the somewhat later leptotene stage shown in 
figure 29 the threads are finer and less homogenous than in the earlier 
stage, the substance of the thread seeming to have become more 
distinctly differentiated into a linin fiber and chromatic granules, the 
latter scattered at irregular intervals along the fiber. Moreover, in 
this later stage the threads appear to be definitely oriented, with one 
end attached at the proximal pole of the nucleus. The threads then 
take a course through the center of the nucleus or near its periphery, 
extending wholly or partly across and then turning back with a wide 
curve. 
2. The zygotene stages.— In figure 30 (Plate 3) some of the threads 
are double, others are single, and it would be difficult to decide from 
a casual examination of this stage alone whether or not the double . 
threads had arisen by a splitting of the single ones. In the case of 
one or two of the double threads, however, as may be seen at the left 
side of the nucleus, the double condition does not continue throughout 
the whole length, but towards the distal end of the nucleus the thread 
is seen to branch into two single threads. I interpret this branching 
thread as one in which the parallel conjugation has not yet been 
completed. Another instance of the same kind may be seen in figure 
31, which represents a stage somewhat more advanced than that of 
figure 30. These appearances lead me to believe that conjugation 
begins at the side of the nucleus corresponding to the proximal ends 
of the leptotene threads, and proceeds gradually toward their distal 
ends. It is further evident from these figures that conjugation is 
