406 Experimental Zoology 
tain from this point of view the female elements. The conclu- 
sion seems plausible, if we believe that the male and female ele- 
ments as such become separated in the spermatozoa and eggs. 
It seems to me, however, that a simpler hypothesis may be for- 
mulated. The sex of the embryo is not laid down as such in 
the egg or sperm, but may be determined later by the quantitative 
relation resulting from the activity of the chromatin in the cells 
of the embryo: not in the sense in which Richard Hertwig has 
expressed this relation, viz. as depending on the size of the 
nucleus, but rather as the result of the increase in the assimilative 
function of cells containing more chromatin material. On the 
other hand, if the number of chromosomes in the unfertilized 
egg of the bee become doubled before segmentation, the fer- 
tilized and unfertilized egg will both produce cells having the 
same number of chromosomes, and it is difficult to see how a 
purely quantitative difference exists. It remains, however, to 
be shown what really takes place in the drone eggs. 
Since all intermediate stages have been found by Wilson and 
by Stevens between cases where the accessory is single and where 
it hasa partner of unequal or of equal size, it may seem probable 
that even when we cannot recognize it by its singleness or by 
its size difference, it is still a sex determinant. This argument 
would be valid if it could be established that unit-characters are 
carried by individual chromosomes; but if the influence of the 
chromatin as a sex determinant is purely quantitative, the argu- 
ment based on a continuous series loses its force; for as soon 
as the difference in size ceases, the quantitative factor disappears. 
However this may be, the importance of the discovery of the 
accessory in sex determination should not be minimized; for 
it is the one clear case in which an internal factor has been 
found that is associated with sex production." 
LITERATURE, CHAPTER XXVI 
(See Chapter XXVII.) 
+ The case of the bee and the ant that have long been known furnish another 
and perhaps a parallel case. 
