ELIMINATION OF SEX CHROMOSOMES 495)". 
and the division is equal in both as in the other chromosomes 
that pass out. This would leave a similar pair (large X and 
small x) in the male-producing egg which becomes the lagging 
pair in the spermatogenesis. This hypothesis works out con- 
sistently but it leaves unexplained the observed size differences 
that appear in the chromosome groups of the male egg; it also 
leaves unaccounted for the production of the smaller male egg 
and it ‘explains away’ the observed size relations in the lagging 
chromosomes of the male egg. Hence I think this view must 
also be put aside. 
Again we might assume that the large X is the sex chromosome 
and the small chromosome attached to it (its synaptic mate) 
is in reality not an X at all, but a Y chromosome. Were this 
the case the Y should pass into the male-producing sperm since 
this is the characteristic behavior of Y in other insects. As it 
does not do so there is no basis of fact to support such an inter- 
pretation. 
Lastly, one may ask whether the two large X’s in the stem- 
mother’s egg are of the same size and also whether the two small 
x’s present are of the same size. Assume for instance that the 
two smaller z’s are unequal in size. If the larger of them should 
pass out into the polar body of the stem-mother’s egg the egg might 
become a male-egg-producer, if the smaller passes out the egg 
might become a female-egg-producer. In this way the two 
lines become differentiated. But this would leave in the female 
line two X’s and one small x (the larger one). We should have 
to assume then that the sexual egg eliminates one large X and 
retains the other large X and the other x (its companion). In 
other words a second differential division must be assumed. In 
the absence of evidence we are scarcely justified in making two 
such assumptions. Moreover, if this view were correct we should 
expect to find a chromosome group in the polar spindle of the 
female producing egg like that in the male-producing egg, but this 
is what we do not find. Of course if the larger of the small 2’s 
that is assumed to be left in the female-egg-producer were much 
larger than that left in the male-egg-producer the size differences 
might not be so marked, but until this can be established we are 
THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 12, NO. 4 
