The sex ratio and oogenesis of Pseudococcus citri. 177 
symbiotic mass, remaining nevertheless in close apposition to it. This 
relative position is maintained until after the revolution of the embryo, 
when the germ cells lying outside of the symbiotic mass again 
leave it, and travel to, and settle on the vaginal invagination which 
arises at this time. Further growth of the invagination then once 
more carries the germ cells or elementary gonads to the symbiotic mass, 
and when this is reached, the final and permanent state of apposition 
is attained. 
I think that it is almost certain that what SHmJr calls primary 
germ cells correspond to the giant cells in my account. The first 
difference in our respective papers therefore lies in what we believe 
to be the nature and origin of these cells. He describes them as 
arising from or close to the place of origin of the germ band, but the 
giant cells always aggregate approximately midway between the anterior 
and posterior poles of the egg. This difference is in itself a slight 
one and may well be due to the fact that SHINJI’s work was done on 
Pseudococcus medanieli, while my own was done on P. eitri and P. 
maritimus. A more important discrepancy, and one which can not be 
reconciled in this way, arises from SHINJI’s considering the cells in 
question as germ cells. If this is true, then the germ cells of Pseudo- 
coecus in this stage carry more than ten, i. e., a multiple number of 
chromosomes. This would be extremely difficult to explain in view of 
somatic, oogonial, and spermatogonial counts which have been made on 
larvae and adults, for, in all these stages, there are ten chromosomes 
in normal cells. It was in an attempt to decide whether SHINJTs 
account could possibly be homologized with my own that the following 
investigation was made of the further development of Pseudococcus. 
As the germ band grows toward the anterior pole, a distinct and 
specially differentiated group of cells can be seen slightly to one side 
of its advancing tip. The cells composing this group are not only 
slightly larger, but are also clearer and stain more lightly than the 
other cells composing the germ band. It is this cell aggregation which 
SHINJI takes to be the rudiment of the midgut. He also describes 
mesoderm cells and ectoderm cells in the band, but these are not con- 
cerned in the present consideration (Fig. 29). Just before reaching the 
symbionts at the anterior pole, the germ band bends and doubles on 
itself, its tip now growing towards the posterior pole again. It is 
through this growth that the typical S form of the embryo is first 
attained. The group of clear cells just mentioned retains its approximate 
Induktive Abstammungs- und Vererbungslehre. XXX. 12 
