MUNSON: SPERMATOGENESIS OF PAPILIO. 
81 
but four chromosomes deep. These seven tetrads are then sepa¬ 
rated (pi. 16, fig. 101). 
Formation o) diads. — Slight traces of linin fibers can finally be seen 
connecting the tetrads, and as they separate more and more, the linin 
becomes more evident. I assume that in the preceding stages, the 
linin has been contracted and formed an imbedding mass in which the 
chromosomes lie. 
The tetrads remain distinct as tetrads only for a short time. As 
they separate they are pulled apart into twos, thus making fourteen 
diads from the original seven tetrads (pi. 16, fig. 103). 
Formation oj the spindle. — As the diads become more and more 
distributed throughout the nuclear space, the linin becomes more 
distinct, while the individual chromosomes of each diad seem to 
diminish in size (pi. 16, fig. 104). Slight indications of a polar arrange¬ 
ment of the linin strands can now r be seen (pi. 16, fig. 105). 
The nuclear membrane now disappears. And this occurs while 
the first undoubted spindle fibers connecting the two centrosomes 
are being formed (pi. 16, fig. 106). The original outline of the nucleus 
is still apparent and the diads are distributed about equally through¬ 
out the nuclear area. All the linin fibers are now, however, much 
more distinct; and a definite polar arrangement is clearly seen. The 
original nuclear area is now slightly elongated in the direction of the 
asters (pi. 16, fig. 106). 
The central part of the spindle is first to be formed. As the remain¬ 
ing fibers are pulled into place, the chromosomes, also, are brought 
into line w T ith the spindle axis. In the meantime the distance between 
the asters seems to increase; hence the oval shape which the spindle 
finally assumes (pi. 16, fig. 107). 
It is very evident that the spindle is of nuclear origin, the entire 
nucleus being gradually converted into a spindle. But that part of 
each spindle fiber extending from the centrosome to the second micro- 
some ring of the aster is of course cytoplasmic in origin as the entire 
asters are. This is seen clearly in plate 16, figure 109, where the 
original nuclear area is still visible. 
Prophase oj first maturation division. — The chromosomes still 
apparently grouped in tw T os when the first signs of spindle formation 
appear, are at first scattered equally throughout the nuclear area, 
and are brought into line at the equator of the spindle as the spindle 
forms. I infer this from such appearances as are represented in, 
