Sex Determination in Phylloxerans and A phids A327] 
neither sex alternative is realized, and that the conditions internal 
or external to which the germ cells are exposed determine which 
one comes to the front. Later in 1905-1906 I argued that the 
determinative conditions are found within rather than without the 
germ cells, and in the case of the bee the determinative factor 
seemed to depend on whether one or two nuclei made up the seg- 
mentation nucleus. If the egg was fertilized the presence of two 
nuclei determined that the female condition evolved; if the egg was 
unfertilized, the single egg nuclei determined that the male condi- 
tion developed. In the case of the hybrid gynandromorphs 
described by Toyama an analysis of the results (1907) seemed to 
show very clearly that a single nucleus derived froma male sperm 
likewise produced male parts. This case furnished strong evidence 
in favor of the view that the results are purely quantitative, and 
are not the outcome of maleness or femaleness, as such, attached 
to the egg or sperm. 
This same point of view advanced for a special case was expanded 
two years later (1907) in my Experimental Zodlogy into a general 
theory of sex determination for those forms in which the two sexes 
had been found to contain more or less chromatin, especially for 
_ Insects with an accessory, and for cases like the bee in which one 
nucleus stands for the male, two for the female. At that time I 
tried to lay special emphasis on the point that the male and the 
female condition represent alternative possibilities of the proto- 
plasm, which one being realized depending on a quantitative fac- 
tor in the cases under discussion. In other words that there is not 
a “segregation” of male from female in the gametes, but some other 
process which leads to the development of one or the other sex. 
This point of view looks upon maleness and femaleness as inherent 
properties of the protoplasm, alternative as to the nature of their 
development. Special factors condition sex in the sense that they 
determine sex, but are not sex “ determinants” in the Weissmannian 
sense. 
In the light of the most recent results we face the further ques- 
tion as to whether these quantitative factors are only more or 
less chromatin or more or less of a particular kind of chromatin 
residing in special chromosomes. An answer to this question 
