348 T. H. Morgan 
CONCLUSION 
The quantitative interpretation of sex-determination is only the 
first rough approximation, I think, to a solution. It is valuable 
because it is supported by a large number of observations in 
which such a quantitative difference is apparent. But there is 
nothing in these facts that shows that the effects are directly 
quantitative rather than that observable quantitative differences 
accompany, or follow in some cases, more profound changes. It 
should not be forgotten, moreover, that the quantitative differences 
have been found in only a relatively small number of cases; that 
they are absent in others, and that in such cases as the male and 
female eggs of phylloxerans where size differences exist in the 
egg as a whole—differences that appear directly associated with 
the formation of the male and the female—the differences originate 
in the presence of the entire number of chromosomes. ‘The loss 
of certain chromosomes from the male egg appears to follow, not 
to precede the size relation. ‘These considerations may arouse 
a suspicion at least that it is not chance that determines to which 
pole the accessory chromosome moves when it is present, but 
that its pole is predetermined. At least the facts here described 
for the phylloxerans and aphids may be urged in support of this 
view. If such differences already exists between the two daughter 
sperms these differences may subsequently be as intimately con- 
nected with the sex of the embryo as the accessory itself. “The 
accessory may follow sex or be associated with other differences 
that determine sex rather than be its sole cause. 
LITERATURE CITED. 
Bearb, F.—The Germ Cells. Zodl.Jahr., xvi, 1902. 
Von Barur, W. B.—Ueber die Bildung der Sexualzellen bei Aphididae. Zodl. 
Anz., Xxxili, 1908. 
Battzer, F.—Ueber die Grosse und Form der Chromosomen bei Seeigeleiern. 
Verhand. Deut. Zool. Gesell., 1908. 
Benpa, C.—Das Problem der geschlechtsbestimmenden Ursachen. Deutsch. 
med. Wochenschrift, 1903. 
