ELIMINATION OF SEX CHROMOSOMES 493 
zation the same chromosome group, which brings back the number 
of chromosomes to that characteristic of the stem-mother, and 
starts the same cycle again in the next year. 
The attachment of the two small x’s to the two large X’s, that 
is assumed to occur throughout this series, except when one of 
the small x’s is supposedly lost in the male-producing line of the 
stem-mother’s egg, and the loss of one large X when the male egg 
extrudes its polar body, may seem to be the most doubtful points 
in the preceding account. That a small x is actually present is 
shown clearly in the spermatogenesis, and in some of the somatic 
cells of the male. It is, therefore, highly probable that the other 
large XY, found in the stem-mother and female line, has also a small 
x attached. Otherwise asymmetrical distribution of the chromo- 
somes can not take place. But my assumption that one small 
x is eliminated from those eggs of the stem-mother that give 
rise to the male line may appear more problematical. I readily 
grant that this is hypothetical. There are two facts, however, 
that give the hypothesis some probability. First, by means 
of this hypothesis the change in observed size-relations that takes 
place in the chromosome group of the male-producing egg can 
be accounted for. Second, the apparent absence of the small 
chromosome, in the lagging chromosome of the polar spindle of 
the male-producing egg, supports this view. On the basis of 
these two observations I have ventured to offer the above hypoth- 
esis, especially as it seems to give a consistent view of the changes 
that take place at the most critical stage in the life eycle when 
two lines are produced. In my former paper I have pointed 
out that there is no external condition that appears adequate to 
account for this dichotomy, and, if this is correct, we are warranted 
in looking for an internal factor that produces the result. The 
assumption moreover is in accord with the view, now well estab- 
lished, that the production of males is associated with the absence 
of. certain chromatin in the egg. From this point of view the 
male-egg-producer—the winged migrant—is half a step towards 
the production of a male; the final step is taken when the other 
X is eliminated, which demonstrably occurs at the next stage 
when the polar body of the male egg is eliminated. 
