276 FRANZ SCHRADER 
follow the same transformations witnessed in the other groups 
mentioned. In contrast to this, the male, which in its somatic 
cells has chromosomes shaped like those found in! the female 
somatic cells, shows no corresponding change in the maturation 
phases. The lengthened form is retained through all the divi- 
sions. This may have no significance, though it does seem to 
indicate an exceptional condition. 
Judging from the evidence at hand, it seems probable that the 
reduction division has been eliminated altogether. It may be 
suggested that the division preceding the final one is also equa- 
tional, and that since there is basically no difference between a 
spermatogonial and an equation division, we are concerned 
merely with a question of names. But our present knowledge 
of the meaning and mechanism of the ordinary equation matura- 
tion divisions is not sufficient to make such a statement altogether 
safe. Furthermore, the assumption of two equation divisions in 
maturation meets with serious difficulties arising from our present 
conceptions of the significance of maturation—a point which will 
be discussed at the end of this paper. 
THE OCCURRENCE OF TRIALEURODES VAPORARIORUM IN 
ENGLAND 
As I have noted in the introduction, although Williams ap- 
parently assumes that normal females of the English line produce 
both sexes when fertilized, such a fact remains to be experiment- 
ally established. Those of his breeding experiments which 
proved successful were made with the exceptional Merton stock 
which resembles the American line in its sex-ratios, and is there- 
fore not of the true or normal English type. 
The parthenogenetic production of females can be explained by 
an omitted reduction division, a reunion of one of the polar bodies 
with the egg-nucleus, or a doubling of chromosomes at some stage 
of development. So far as we know, the sperm nucleus of ani- 
mals does not attempt union with the nucleus of the egg until 
the latter has undergone the maturation process. I think there- 
fore, that it is only fair to assume that the spermatozoon may 
very well enter the egg of mated females of the English race, but 
that it plays no further réle unless reduction takes place. 
