The sex ratio and oogenesis of Pseudococeus eitri. 171 
mosomes go to each pole. The two daughter groups of chromosomes 
are situated in two distinct protoplasmic areas, but although the mitotic 
spindle of the division figure is sometimes at an angle with the edge of 
the egg, both areas are finally found at the periphery (Fig. 16 and 17). 
leven clear figures of this first division of the polar nucleus show that 
the process is always a normal one so far as the cytological evidence 
is concerned. Similarly, the indications are that each group of fifteen 
chromosomes resulting from it sometimes undergoes a second normal 
division, so that four such groups are then found at the periphery. 
It is during these first divisions of the polar nucleus, that the 
cleavage cells begin to approach the periphery, where, up to this time 
only the polar bodies or their derivatives have been located. In the 
cleavage cells, division occurs much more rapidly than in the polar 
nucleus; so that after the completion of the first division of the polar 
nucleus there may be as many as twentyfour cells in the interior of 
the egg. Each of these has ten chromosomes. Before the initiation 
of the second division of the polar nucleus, the first of the cleavage 
cells have reached the periphery. However, even after the migration 
of the cleavage cells has apparently been completed, some cells are 
found in the yolk which at that time differ neither in the number of 
chromosomes nor in any other way from the cells that have reached 
the edge of the egg. These are the so-called yolk cells. 
Although the first one or two divisions of the polar nucleus 
appear normal, later divisions of the polar nucleus derivatives are 
subject to irregularities. Apparently nuclear division is then very 
often or even generally not accompanied by cytoplasmic division, so that 
the two resulting nuclei may lie side by side in a single protoplasmic 
area. At the ensueing division, there may be an intermingling of the 
chromosomes evolved, or else a multiplicity of spindles. Possibly also, 
cleavage cells nearing the edge may at times fuse with the derivatives. 
As a consequence, nuclei showing thirty or more chromosomes are 
typical (Fig. 18). Such irregularities are seen to even better advantage 
in Pseudococcus maritimus (SCHRADER, 1922). 
Division in the polar nucleus derivatives proceeds, in spite of the 
multiple number of chromosomes, until they occupy a considerable area 
at the periphery of the egg. Separated at first, they gradually form a 
continuous layer, one cell in thickness. Thus in a sagittal section 
through the middle of the egg, almost one half of the periphery may be 
taken up with these cells, the rest of the periphery being covered now 
