Sex Determination in Phylloxerans and Aphids 251 
larger cell even before the accessories have quite approached that 
region. As they move in, they, with the rest, become enclosed in a 
common nuclear wall. 
This first spermatocyte division is of unusual significance. 
Hundreds of nuclear stages have been examined, and they all tell 
clearly the same story. It is certain that the accessories do not 
divide, but pass entire to one of the two cells formed at the first 
spermatocyte division. It is true that they are somewhat elon- 
gated at one stage, and sometimes give an impression that they are 
about to divide; but later they contract and pass over entire into 
the larger cell. 
The resting stage following the first division is shown in Fig. 
VI, L-M. In many cases all six chromosomes can be counted 
in the larger cells. The small cells come to lie in the corners 
between the larger cells, or often at the outer wall of the follicle. 
The chromosomes form a dense mass, staining deeply in iron 
hematoxylin. Their presence in a follicle shows that the cells 
have passed through the first division—a point not easily made 
out from the size of the larger cells alone since these, from their 
mode of origin, necessarily approach closely the size of the pre- 
spermatocyte cells. 
Equatorial plates of the second spermatocyte are relatively 
less abundant. Some of them are represented in Fig. VI, N-Q. 
Four of the chromosomes are sometimes seen to be smaller than the 
other two—owing to the non-division of the latter. “he chromo- 
some plate is more compact, and it is difficult to obtain cases where 
the chromosomes are distinct. 
At the second spermatocyte division all the chromosomes of 
the larger cells divide equally. There are none that lag behind the 
rest (Fig. VI, R-U). Two equal cells result, and these become 
spermatozoa, each carrying six chromosomes. 
The small rudimentary cells, present after the first spermatocyte 
division, do not divide, as far as I have observed, at the time when 
the large second spermatocyte cells divide. “They remain in the 
follicles as dark bodies which can be identified for some time later 
when they disappear without producing spermatozoa. 
\Z Let us return to the female line. We have seen that the polar 
