OOGENESIS IN PHILOSAMIA 13 
c. Development of nurse cells 
A condition shown in figure 45 succeeds that of the preceding 
figure. The spireme is spread out through the nuclear cavity, 
and appears to consist of about 13 segments, most of them looped, 
but without any indication of polarization. A small plasmo- 
some is present. Somewhat later (fig. 46), 13 definite segments 
may be counted, and the loops show a tendency to straighten 
out into long rods. The threads are very definite, with fairly 
smooth outline, and appear very slightly thicker than when 
first opening out. The haploid number was counted in at least 
twenty nuclei of this period. The plasmosome is slightly larger 
than before, and has no chromatin associated with it, nor is 
there any orientation of the segments with respect to it. To- 
ward the latter part of this stage, the nucleus increases in size, 
and the chromatin segments gradually become thicker and more 
deeply-staining, .giving rise to the condition shown in figure 
47. Some of the segments are in the form of curved rods, others 
are sharply bent. The plasmosome is larger at this time, and 
frequently vacuolated. 
The condition of the thick threads in figure 47 is similar in 
general appearance to the pachytene stage of other animals, 
but it is probably not equivalent in its origin, since the threads 
are formed, not by doubling, but by a gradual widening of the 
thinner threads. This stage represents the pachytene period 
only in the sense that it is subsequent to synapsis, and gives 
rise to the diplotene stage. 
Stage g (figure 48): The diplotene stage. A longitudinal 
split now appears for the first time in all the chromosomes, 
and shows very clearly in cells which lie directly in contact with 
‘those of the preceding period which show no split. They are 
differentiated from them also in length of the chromosomes, 
for the split threads are considerably shorter. Doncaster (712) 
describes in Abraxas the double thread as arising probably by 
a bending over of the chromosome, with a separation later at 
the bend, but this is certainly not the case in P. cynthia. There 
is no clue whatever to the relation of these double threads to 
