Sex Determination in Phylloxerans and Aphids 305 
or possibly double. I count 9g, 10 and 11, but the clearest cases 
(Fig. XXIII) give 10 chromosomes and this | believe to be the 
typical number. A late stage in the division of the first spermato- 
cyte is figured in Fig. XXIII, J. 
This species shows clearly, however, in the oogenesis a stage 
that resembles the synapsis stage of other insects. It is shown in 
Fig. XXIII, ‘f-K. ‘These ova are found in the bottom of the ovary, 
and probably become the sexual eggs. If this were not the case, 
a synapsis stage would be passed through even in eggs that re- 
tain the full number of chromosomes. It has been stated in fact 
that this process occurs in the parthenogenetic eggs of aphids, 
but this requires confirmation. 
CYTOLOGICAL PARALLEL BETWEEN PHYLLOXERA CARYECAULIS 
‘ AND SYROMASTES MARGINATUS 
Wilson has pointed out recently the striking resemblances in the 
chromosomal cycle between these two species, and the comparison 
removes what might otherwise have proved to bea very anomalvuus 
condition in one of the two forms here described. The diagram 
which Professor Wilson has constructed (1909) will show at a 
glance the points of comparison. 
The comparison depends primarily on the behavior of the two 
accessories and is independent of the interpretation as to their 
origin. Wilson adopts the view that in this case two chromosomes 
are the product of division of one accessory, rather than an original 
pair that now move to the same pole. [n support of this interpre- 
tation he points to the series of species described by Payne in 
which one, two, three or four chromosomes form one group, 
with which a single chromosome still forms “a pair.” 
In Syromastes there are two accessory chromosomes of unequal 
size a.+ 6 as in P. caryzecaulis and these unite when they pass 
into the “female producing” sperm. In the female there are two 
pairs of homologous chromosomes, a + a, b + 6. Presumably 
these pair with each other during synapsis and subsequently 
separate when the polar bodies are formed giving a + b for the 
egg and a + b for the polar body. ‘The female sperm brings in 
