18 
W. E. AG Alt. 
valents). Of tlie bivalents four are closed rings 1 (bl-bV), 
three of the others have their constituents separated except at 
one point of contact (b5-b7), and in two of them the ex-con- 
jugants have almost completed their separation (si, s2). 
In PI. 3, fig. 23, the fact that the transverse constrictions 
are only incipient in many of the chromosomes makes it 
difficult to value them, but it is certain that there is a mixture 
of uni- and bi-valents, the former predominating. 
At the time that the nuclear membrane disappears separa- 
tion of the ex-conjugants is generally complete, and we have 
thirty-eight quite free univalent, transversely constricted 
chromosomes (PL 3, fig. 24). As regards this constriction, 
it may be said at once that it does not represent a future 
division plane of the chromosome (see pp. 22, 29). 
As the individual chromosomes become free from the 
synizetic mass they tend to become arranged close under the 
nuclear membrane, leaving the centre of the nuclear space 
empty. This condition of peripheral distribution of the 
chromosomes shortly before the disappearance of the mem- 
brane is a widely distributed phenomenon, but in the case of 
the meiotic prophase it is usual to find them in the reduced 
instead of the somatic number. Indeed, this is often the 
stage at which the peculiar shapes of the bivalents (rings, 
crosses, tetrads, etc.) is best made out. 
During the period covered by the last few figures the 
nucleolus, which was such a conspicuous object until it was 
hidden in synizesis, gradually loses its staining capacity, 
becomes irregular in outline, and disappears. 
Just before the dissolution of the nuclear membrane the 
diameters of the nuclei vary round an average of about 35 fi . 
When the membrane disappears we get the condition shown 
in PI. 3, fig. 24. At this stage no achromatic figure can be seen 
1 It must be remembered that this nucleus, like all the others about 
this stage, was examined and drawn from both sides. In the case of 
the rings bl-bo, which are seen in end view, it is difficult to give proof 
of their ring nature in the figure, though this is at once apparent on 
examination of the same chromosome from both surfaces. 
