Sexual Nuclei in Lilium Mar tag on. 461 
doing so they cluster together at one side of the nuclear 
cavity round the half-dissolved nucleolus (Figs. 17, 18). The 
nuclear membrane at the same time becomes indistinct. All 
the phenomena of synapsis have in fact reappeared. After 
contraction has proceeded for some time each filament shows 
a double, not a single row of dots. The stage at which this 
can be clearly made out depends a good deal upon the 
preparation. That from which Fig. 18 is drawn, for instance, 
suggests a double row on careful examination, but the thick- 
ness of the section prevents absolute certainty. At a rather 
later stage the double row of dots can be quite clearly seen 
in microtome sections. I am inclined to believe that the 
actual fission of the original single row of granules in each 
filament takes place very shortly after the longitudinal 
splitting of the spirem ribbon. This is the second occasion 
on which we have found the phenomena of synapsis 
associated with the fission of a row of chromatin granules. 
The double filaments may now be called chromosomes. 
They continue to shorten and broaden, and soon acquire the 
appearance represented in Fig. 19 a. Contraction indeed 
continues up to maturity (cf. Fig. 20 with Fig. 19), but shortly 
before that time a curious change in the structure of the 
chromosome takes place. Chromatic dots can no longer be 
distinguished on segments of linin ribbon. The whole chro- 
mosome stains uniformly like chromatin. I cannot even 
make out whether a fission in each mature segment corre- 
sponds to the interval between the two rows of chromatin 
granules. Each segment looks perfectly homogeneous. 
One effect of this change is to make it much more difficult 
to distinguish between the segments of a single chromosome. 
The twist of the segments on each other naturally becomes 
closer during contraction, but while the outline of each was 
traced by a row of dark dots the compound character of the 
chromosome was clear. After the segments have become 
uniform in colour it is only in favourable cases that their 
twist on each other can be made out at all (Figs. 20, 21). 
Little remains to be said as to the behaviour of the 
