10 
SIDNEY I. KORNHAUSER 
to one centrosome; a minute degenerate non-chromatic globule 
is formed at the other pole of the spindle. In the second matura- 
tion division, the chromatin divides, but one of the spermatids 
is very small and degenerates. Thus only one instead of four 
spermatids is formed, and it contains the haploid number of 
chromosomes. Variations of this process are found in other 
Hymenoptera, resulting frequently in two spermatids from the 
larger second spermatocyte, each possessing the haploid number 
of chromosomes. 
The possibilities of sex production through parthenogenesis are 
many. Reduction to the haploid number, or the elimination of 
a whole X-chromosome, may produce a male, whereas the elimi- 
nation of one maturation division may allow the egg to retain 
the diploid number and develop into a female. Still further 
possibilities are offered in cases where either the retention of the 
Z-chromosome or its elimination is of vital concern in the 
resulting offspring. Goldschmidt has reared both sexes from 
unfertilized moth eggs. 
4 . POLYEMBRYONY 
Closely allied to the subject of the chromosomal basis of sex 
are the facts of polyembryony. Where more individuals than 
one are formed from an ovum they are almost invariably of the 
same sex. The classical examples are parasitic Hymenoptera, 
principally of the families Procotrypidae and Chalcididae, where 
often thousands of individuals result from a single egg. Other 
examples are the quadruplets formed in the nine-banded armadillo, 
and identical or monochorial twins in man and other mammals. 
In the case of mammals the type of sperm (either with or without 
an X-chromosome) is undoubtedly the deciding factor. Pro- 
viding then that all the chromosDmes of the zygote divide nor- 
mally, the sex of the resulting individuals must be the same, 
and they will be genetically identical. In the Hymenoptera the 
sex will depend entirely on fertilization or parthenogenesis. A 
fertilized egg will result in females and an unfertilized ovum in 
males. Patterson has occasionally got one or a few males in a 
