80 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
History of the chromatin .— The chromatin nucleolus has now dis¬ 
appeared, but the nuclear network seems still unchanged. The chro¬ 
mosomes are still irregularly scattered throughout the nucleus; and 
apparently connected with the linin strands. These are granular 
as usual. 
A change now ensues. The loose wavy linin strands become con¬ 
verted into a well defined system of straight intersecting threads by 
which the chromosomes are suspended about equidistant from one 
another. The linin threads seem stretched, and the chromosomes 
are more regular and more clearly defined than previously (pi. 16, 
fig. 93). 
Formation oj the spireme .— What up to this time appeared as a 
network, has now been converted into a single coil, with the chromo¬ 
somes arranged like a bead string. The coil is wavy and as it does 
not lie in the same plane, it is difficult to understand and even more 
difficult to represent in a drawing (pi. 16, fig. 94). 
The thread then becomes closely packed in a solid mass at one pole 
of the nucleus (pi. 16, fig. 95). The point of condensation seems to 
vary as it is not always found at the same pole, considering the position 
of the asters. 
This mass then moves into the center of the nucleus (pi. 16, fig. 96). 
It now consists of a double thread — two parallel rows of chromosomes 
— wdiich viewed in the right plane has more or less the shape of a 
horseshoe or imperfect circle. This then elongates (pi. 16, fig. 97) 
and the result is a second doubling of the thread, making a thread of 
four chromosomes lying side by side (pi. 16, fig. 98). Very little of 
the linin is to be seen between the chromatin. The rest of the nucleus 
is a clear vacuole. I have discovered no definite relation between the 
position of this chromatin thread and the axis uniting the two cen- 
trosomes. 
Formation oj tetrads .— The chromatin thread now begins to break 
up, and the fragments separate gradually (pi. 16, figs. 99, 100). Each 
fragment consists of four chromosomes (pi. 16, fig. 101). As they do 
not all lie in the same plane, they are not all visible at the same time. 
Hence some of the chromosomes of a tetrad seem less distinct than 
others. No clear linin fibers connecting the tetrads are visible. 
The tetrads are thus formed from a single chromatin thread doubled 
twice on itself. There being originally twenty-eight chromosomes, 
the thread when thus doubled shows seven chromosomes in a line, 
