The sex ratio and oogenesis of Pseudococcus citri. 179 
which characterize them, and which distinguish them very clearly from 
all of the cells in the germ band at least. The only cells which might 
be confused with them are the yolk cells. As has been pointed out, a 
few of the latter may now and then join the giant cells and escape 
recognition; but this would be of little significance because migration 
towards the periphery is not a general movement in the relatively small 
number of yolk cells that are found in the average egg. In describing 
certain cells around or in apposition to the symbionts during growth 
of the germ band, SHINJI probably has in mind the phase during which 
the giant cells have not yet entered into complete association with the 
symbionts—a phase shown in Fig. 22 or 23 of the present paper. In 
the meantime he is fully aware of the aggregation of clear cells close 
to the tip of the growing germ band. This he interprets as the 
rudiment of the midgut, overlooking entirely the stage prior to the 
revolution of the embryo when these cells do not accompany the growing 
tip of the germ band and are left behind. Certainly he is correct in 
claiming that the midgut originates from the cells at or near the tip 
of the germ band, but the clear cells that were seen there at an earlier 
stage are not identical with the midgut cells later found at that location. 
It is peculiar that after revolution of the embryo SHINJI recognizes the 
true germ cells as such. They are then still in the identical place on 
the germ band, having undergone no change of location in respect to 
it since first separated from the growing tip, and showing no change 
in appearance. SHINJI, however, under the impression that they have 
previously been in apposition to the symbionts, interprets their location 
on the germ band as being due to a migration from the former to the 
latter position. From this point on, his interpretation coincides exactly 
with mine. It thus appears as definitely established that the germ 
cells and the cells associated with the symbionts—the giant cells—are 
definitely distinct cells, separated throughout the period during which 
their final condition and location are established. 
I gladly express my thanks to Dr. Chas. H. RICHARDSON, of 
Washington, D.C., whose kind help during the year 1920 made 
possible the continuation of the breeding experiments while I was 
unavoidably absent. 
Summary. 
1. Virgin females of Pseudococeus citri do not give rise to 
offspring. 
12* 
