36 Overton . — On the Organization of the Nuclei in the 
membrane disappears, in which the chromosomes are all short parallel 
double rods. Figs. 17 a-ij c, PI. Ill, show some conditions rarely observed 
in which these rods are arranged endwise or crossed to form an X-shaped 
figure. The most usual arrangement is that of parallel double rods 
(Fig. 17*, PL III). 
In diakinesis the longitudinal splitting of each component of the bivalent 
chromosomes occurs or becomes at first evident. This split apparently takes 
place before the diakinetic chromosomes become much shortened and 
thickened (Fig. 14 e, PI. III). Each component of the parallel double rods 
splits lengthwise throughout its whole length, at right angles to the plane of 
approximation, giving rise to four parallel rods, or the so-called four-parted 
chromosomes (Fig. 1 6 a, PL III). When the diakinetic chromosomes become 
completely shortened and thickened, this split in each component is appa- 
rently obliterated for a time (Fig. 1 j b, PL III). In Fig. 16 b, PL III, the 
four parts are also distinctly visible, but are differently oriented with reference 
to each other, forming an X-shaped figure with each arm of the X consisting 
of two parallel portions. In some cases the halves of each univalent portion 
may become more or less separated from each other at this period, so that 
various figures may arise depending upon the relative positions of the two 
split portions of the chromosomes. If these are placed end to end (Fig. 1 y a, 
PL III), the four portions may spread apart at their inner juncture, forming 
a double V-shaped figure with the two halves facing each other (Fig. 1 6 c, 
PL III). 
The arrangement of the chromosomes in the equatorial plate and their 
separation during metaphase are similar to those which I have described for 
Thalictrum and Calycanthus . The multipolar spindle (Fig. 18, PL III) 
later becomes bipolar (Fig. 19, PL III), and its poles are rather more 
pointed than in Thalictrum. Fig. 20, PL III, shows a polar view of the 
equatorial plate, with the sixteen chromosomes placed in different planes. 
In Fig. 19, PL III, which is a side view of the same, the majority of the 
chromosomes are shown in late metaphase. Some chromosomes in this 
figure are shown as having already separated, and as just beginning to pass 
to the poles. P'igs. 21 a-21 c, PL III, show the various forms of the hetero- 
typic chromosomes during metaphase. As the chromosomes pass toward 
the poles of the spindle, they show distinctly as two-parted structures 
(Figs. 23^-23;/, Pl. III). 
In studying Richardia I have especially focussed my attention upon 
the arrangement of the chromosomes and their behaviour during the recon- 
struction of the daughter nuclei. This plant furnishes especially favourable 
material for the study of the nuclear structure during these stages. As the 
sixteen, short, rather thick, two-parted chromosomes approach the poles, 
they are widely separated from each other. They keep this arrangement 
as they arrive at the poles (Fig. 24, PL III). As development proceeds 
