The sex ratio and oogenesis of Pseudococeus citri. 175 
PETRUNKEWITSCH (1903), in his much discussed paper on maturation 
in the bee’s egg, described the union of the second polar body with 
the inner group of the divided first polar body, and claimed that the 
germ cells were derived from this “Richtungskopulationskérper”. It 
is this last point which has met with much criticism. NACHTSHEIM 
(1913) confirms PETRUNKEWITSCH in his observations on the fusion of 
polar bodies, but believes that the derivatives of this polar nucleus, 
after undergoing a period of irregular division, always degenerate 
and disintegrate. Although this and similar criticisms have made 
PETRUNKEWITCH’s interpretation of the origin of germ cells very 
doubtful, the fact seems nevertheless established that the polar nucleus 
in the bee’s egg is not subject to immediate disappearance. A much 
clearer case of functional polar bodies, however, is furnished by various 
members of the Hymenopteron family of Chalcididae. SILVESTRI (1906 
and 1908), MARTIN (1914), and more recently PATTERSON (1921) have 
all described the union of polar bodies in the eggs of various species 
of these polyembryonic insects, and all agree that it is this polar 
nucleus which plays an important part in the partition of the mass of 
cleavage cells into distinct embryonic masses. In view of such cases 
it is indeed possible that persistence of polar bodies may not be as rare 
as has hitherto been assumed. The phenomenon might be expected 
especially in parthenogenetic eggs where the pronucleus itself is certainly 
not dependent on the sperm in any way. It is true that I have found 
no evidence of such a development in Trialeurodes and Tetranychus, 
both cases of haploid parthenogenesis; but in neither was the fate of 
the polar bodies a factor in the investigation, once they were formed 
or given off. It is clear that in any case, CONKLIN’s explanation that 
polar bodies do not develop because of the absence of a sperm can 
hold neither in parthenogenetic nor polyspermic eggs. 
The above account also clears up the peculiar character of the 
cells associated with the symbiotic spheres in the bodies of embryos and 
adult females, and explains at once the multiple number of chromosomes 
always found in such cells. That such cells are found in similar 
association in other Homoptera is possible, although of course I am not 
prepared to claim a parallel origin in such other cases. In Trialeurodes, 
a multiple number of chromosomes is certainly to be found there 
(SCHRADER, 1920); but, as | have indicated, no detailed investigation 
was there made on that point. BUCHNER (1918) has made a more 
careful study of the history of the symbionts in the related Aleurodes, 
