A Study of the Chromosomes in thiee species of Pseudococcus. 
47 
the nucleus is taken up by a soraewhat more deeply staining mass, defini- 
tely distinct front the looser chroinatin just mentioned. In P. citri and 
P. nipae no detailed stmcture could be inade out in this mass (Fig. 27), 
but preparations of P. maritimus show it to be interspersed with denser 
knots, indefinite m number. Knots which are comparatively more dense 
are also found in the more üghtly staining chromatin so that the two 
materials in a nucleus at this stage differ superficially only in the inten- 
sity with which they stain (fig. 1). 
Brief mention may be made here of the nucleolus which is at this 
time visible in P. citri and P. maritimus. This is comparatively larger 
in the last named species. In both cases it decreases rapidly in size in the 
succeeding stages and has disappeared when the first division takes place. 
The next stages are shovm in fig. 2 and 28. The lightly staining 
chromat n has begun to fomi threads while the material of the more 
deeply stained chromatin begins to be segregated in irregulär masses. 
Whether the latter then form a spireme is not certain. The view shown 
in fig. 29 would indicate that at least long threads are certainly formed 
from this mass in P. citri. No good figures that paralleled such a stage 
were found in the other two species. For a limited time the lightly stai- 
ning threads seem to be polarized toward that part of the nucleus where 
the denser chromatin material is located. Indications of this were found 
in P. citri and P. nipae, but in P. maritimus there was no clear indication 
of such polarization at this stage. At best it can be a period of only 
very short duration. However this may be, at the time when the denser 
chromatin has formed definitely segregated lunips or eise short, coarse 
threads, all traces of polarization have disappeared and the lightly staining 
threads are scattered through the nucleus vithout any definite arrange- 
ment (fig. 3 and 29). There is no evidence of a conjugation of threads 
during these stages or at any other time. 
It soon becomes established beyond a doubt that the bodies oiigi- 
nating from the dense chromatin are perfectly definite in number, and 
this in all cases is five. They appear as thick thi*eads, rough in contour, 
and are chraracterized by a longitudinal split which first becomes defini- 
tely visible at the stage shown in fig. 2. Moreover, these bodies have the 
tendency to remain in dose proximity to each other and to the nuclear 
wall. This tendency to be crowded together is very marked in P. mariti- 
mus and P. nipae, and less so in P. citri. In the latter, the massing is 
not emphasized after the earliest stages and occasionally these five bodies 
may be separated as widely as shown in fig. 30 which presents a polar 
view of this group. But even in extreme cases of scattering, careful 
