nuclei of the female must be alike so far as number and size of
chromosomes are concerned, while it is absolutely certain that the
spermatids are of two equal classes as to chromatin content of the
nucleus--one-half of them have 9 large chromosomes and 1 small one,
while the other half have 10 large ones. Since the male somatic cells
have 19 large and 1 small chromosome, while the female somatic cells
have 20 large ones, it seems certain that an egg fertilized by a
spermatozoon which contains the small chromosome must produce a male,
while one fertilized by a spermatozoon containing 10 chromosomes of
equal size must produce a female. The small chromosome itself may not be
a sex determinant, but the conditions in _Tenebrio_ indicate that sex
may in some cases be determined by a difference in the amount or quality
of the chromatin in different spermatozoa. This is much the most
suggestive part of the work, and it will be followed up by the study of
related forms.

There appears to be so little uniformity as to the presence of the
heterochromosomes, even in insects, and in their behavior when present,
that further discussion of their probable function must be deferred
until the spermatogenesis of many more forms has been carefully worked
out.

BRYN MAWR COLLEGE, _May 15, 1905_.

BIBLIOGRAPHY.

BAUMGARTNER, W. J.

'04. Some new evidences for the individuality of the
chromosomes. Biol. Bull., vol. 8, no. 1.

MCCLUNG, C. E.

'99. A peculiar nuclear element in the male reproductive
cells of insects. Zool. Bull., vol. 2.

'00. The spermatocyte divisions of the Acrididae. Kans. Univ.
Quart., vol. 9, no. 1.

'01. Notes on the accessory chromosomes. Anat. Anz., bd. 20,
nos. 8 and 9.

'02. The accessory chromosome--Sex determinant? Biol. Bull.,
vol. 3, nos. 1 and 2.

'02_a_. The spermatocyte divisions of the Locustidae. Kans.
Univ. Quart., vol. 1, no. 8.

MONTGOMERY, THOS. H., JR.

'01. A study of the chromosomes of the germ-cells of
Metazoa. Trans. Amer. Phil. Soc., vol. 20.

'01_a_. Further studies on the chromosomes of the _Hemiptera
heteroptera_. Proc. Acad. Nat. Sci. Phila. 1901.

'04. Some observations and considerations upon the
maturation phenomena of the germ-cells. Biol. Bull., vol. 6,
no. 3.

MOORE, J. E. S., and ROBINSON, L. E.

'05. On the behavior of the nucleolus in the spermatog