Opalina. . 235 
masses of chromatin may be slower than the rest in coming to 
the center of the nucleus and in taking their place in this double 
transverse row, but in the end all do so. 
Each chromatin mass is connected with the pole of the nucleus 
by one, or sometimes by two, of the thicker chromatin fibres (Fig. 50). 
The chromatin masses of the two groups are also connected with 
one another by thick fibres which cross the equator of the nucleus. 
Occasionally one sees a fibre start from a chromatin mass, cross 
the equator of the nucleus and pass on directly to the opposite pole 
without connecting on the way with a second chromatin mass (Fig. 50). 
This, however, is not very general. One may say that the chro- 
matic spindle is composed of fibres which in general stretch from 
pole to pole of the nucleus and connect in their course with one or 
two chromatin masses. The fibres may branch and unite in a more 
or less irregular way. 
The chromatin masses now begin to migrate toward the poles 
of the nucleus (Figs. 53—55, 58, Pl. XVIII). During these migration 
stages, one often sees that the chromatin fibres connecting the chro- 
matin masses with the poles are thicker, while the fibres stretching 
across the equator are fainter (Fig. 54, Pl. XVIII; 0. caudata, Fig. 81, 
Pl. XX). During this migration the chromosome masses assume more 
definite shape, becoming in general more elongated (Fig. 58). They 
lie side by side and because of their regular arrangement and com- 
pact form are best studied at this stage. They seem to be true 
chromosomes. They keep their regular parallel position during the 
whole migration, but, as thy approach the pole, first some and then 
others may divide into two (Fig. 54), and at about the same time 
they send out thin broad plates of chromatin which unite them 
together (cf. the upper end of the nucleus in Fig. 58). The stage, 
then, when the chromosomes can be counted and studied to best 
advantage, is but a brief one during the middle portion of the 
migration. As some chromosomes may be late in coming into the 
double transverse equatorial plate, and as others may divide pre- 
cociously during the migration, one finds, in certain nuclei, conditions 
that are very confusing. I have, however, carefully counted the 
chromosomes in more than a hundred favorable nuclei in the middle 
anophase condition and find their number to be eight for O. m- 
testmalis (Figs. 32, 33, 36, Pl. XVI; 58, Pl XVUI; 65, Pl. XIX; 
119, Pl. XXII, anterior nuclei of 201—-203, Pl. XXIV). The apparent 
exceptions are due, I believe, wholly to precocious division of the 
chromosomes, or to their precocious fusion by means of the band- 
