8 PAULINE H. DEDERER 
At a later period, it is possible to count the chromosomes in 
each nucleus. In figure 35 the pronuclei lie near the surface 
of the egg where the second polar body appears. The surface 
cytoplasm merges with the remnants of the vitelline mem- 
brane, in which the polar body lies. Figure 27 is the same sec- 
tion enlarged. The pronuclear walls appear broken at the 
region of contact, or are so thin as to be invisible. Nine chromo- 
somes are seen in the first section of the outer nucleus, 11 in the 
first section of the inner; they differ s ightly in size, and some 
are noticeably dyad in form. To the right of these are drawn 
portions of the nuclei from a succeeding section, showing 4 more 
chromosomes in the outer nucleus, 2 more ‘n the inner, making 
13 in each. No nucleoli are present. Within the polar body 
figured here remains of spindle fibers and a nuclear membrane 
are seen. Here too, 13 chromosomes appear. This is probably 
the second polar body, for the first becomes very vague after the 
second anaphase. 
In figure 28, from an egg similar to the one described, nine or 
more chromosomes may be counted in the second polar body. 
The first polar body has apparently divided, the chromosomes 
in each appearing as vague granular areas. It seems probable 
that all three degenerate shortly after the fusion of the germ 
nuclei. There is no evidence that they remain included within 
the egg. 
2. CONCLUSIONS AND COMPARISONS 
The evidence obtained from the foregoing study indicates 
that in Philosamia cynthia the 13 chromosomes seen in the 
late prophase of the egg all divide in both maturation divisions. 
The male and female pronuclei at the time of their union each 
contain 13 chromosomes, giving the somatic number 26, which 
is found in the nuclei of the blastoderm. It appears to be certain 
that all of the eggs contain the sanie number of chromosomes, 
but the evidence for either the presence or absence of an X Y-pair 
is not conclusive, on account of the variability in the size of the 
chromosomes in the metaphase and anaphase plates. In the 
early oogenesis, to be described later, there is no indication of 
