OOGENESIS IN PHILOSAMIA 9 
the presence of a heterochromosome, either of equal or unequal 
parts, and from this we might suspect its absence in later stages. 
Although from the totality of the evidence, it appears probable 
that there is no difference in the chromosome groups, the matter 
will have to be left an open question. 
Doncaster (12) found that in Pieris brassicae both the male 
and female germ cells contain an equally paired heterochromo- 
some which constitutes a chromatin nucleus during the growth 
period. He believed that in Abraxas a similar condition prob- 
ably prevailed, and concludéd that the chromosomes here ‘‘do 
not provide any visible basis for the sex-limited transmission 
of characters.’ More recently, however (’13) he has found 
some females of Abraxas with 56 chromosomes, some w th 55, 
and he believes that there s a possibility of two kinds of eggs 
in this form. 
Until the past year, the only recorded case of nuclear dimor- 
phism in eggs (exclusive of parthenogenetic and sexual eggs) 
was that of the sea-urchin described by Baltzer (’09), in which 
the female appeared to be the heterogametic sex. Tennant, 
(12) however, discovered that in other forms the male is hetero- 
gametic. Baltzer has recently ('13) announced that the results 
- described in his former paper are erroneous, and he is convinced 
that the male is the heterogametic sex. This solves the apparent 
contradiction within the echinoderm group, the females being 
homozygous for sex in all cases described. 
The latest case of heterogamy in the female is that recently 
described by Seiler (’13) for the lepidopteran Phragmatobia 
fuliginosa. In the spermatocyte divisions, 27 small chromo- 
somes are present, and a large one, which, though lagging some- 
what, divides equally in both maturation divisions. In the 
first metaphase plate of the egg, 27 small chromosomes and a 
large chromosome, slightly segmented or lobed appear. After 
the first division, at one pole of the spindle are seen 27 small 
chromosomes and a large one; at the other pole, 28 small chromo- 
somes and a large one. It is a matterof chance whether the polar 
body or the egg nucleus receives the extra chromosome. Seiler 
interprets the extra small chromosome as a lobe of the large 
