mosome in the male being less
active. The first of these alternatives is an attempt to cover such
cases as _Dinophilus_, _Hydatina_, and _Phylloxera_ with large female
and small male eggs. Here Morgan's ('06) suggestion as to degenerate
males seems much to the point. The male sex character, having become
dominant in certain eggs at an early stage, may, from that time on,
determine the kind of development. As to the second alternative, I see
no reason for supposing that the small heterochromosome of a pair is in
any different condition, as to activity, from the large one. The
condensed condition may not mean inactivity, but some special form of
activity. And, moreover, it has been shown that in certain stages of the
development of the oocyte of one form, _Aphrophora quadrangularis_,
there are pairs of condensed chromosomes corresponding to those of the
spermatocyte, so that there would hardly seem to be any basis for
Wilson's attempt to associate the difference in development of male and
female germ cells with activity or inactivity of chromosomes, as
indicated by condensed or diffuse condition of the chromatin.

On the whole, the first theory, which brings the sex determination
question under Mendel's Law in a modified form, seems most in accordance
with the facts, and makes one hopeful that in the near future it may be
possible to formulate a general theory of sex determination.

This work has been done in connection with a study of the problem of sex
determination, but, whatever may be the final decision on that question,
it brings together a mass of evidence in favor of the belief in both
morphological and physiological individuality of the chromosomes, as
advocated by Boveri, Sutton, and Montgomery. It also gives the strongest
kind of evidence that maternal and paternal homologues unite in synapsis
and separate in maturation, leaving the ripe germ cells pure with regard
to each pair of characters.

BRYN MAWR COLLEGE, _June 7, 1906_.

FOOTNOTES:

[B] AUG. 20, 1906.--36 species belonging to 12 families. See note, p.
49.

BIBLIOGRAPHY.

BOVERI, TH.

'02. Ueber mehrpolige Mitosen als Mittel zur Analyse des
Zellkerns. Verh. d. phys.-med. Ges. Wuerzburg, N. F., vol.
35.

CASTLE, W. E.

'03. The heredity of sex. Bull. Mus. Comp. Zool. Harvard
College, vol. 40, no. 4.

MCCLUNG, C. E.

'99. A peculiar nuclear element in the male reproductive
cells of insects. Z