The sex ratio and oogenesis of Pseudococcus eitri 169 
The first maturation division takes place parallel to the periphery 
and results in two groups of five dyads each (Fig. 4). It is a peculiar 
feature that the two unit components of each dyad are seemingly only 
loosely connected, and after the early telophase in which each dyad 
lies separately in a clear area (Fig. 5), these units often are situated 
some distance apart. In every case at this stage, a dark disc-like 
structure is found between the two groups of dyads. The formation 
of this is begun already in the anaphase, and | regard it as a spindle 
rest (Fig. 6). 
One of the chromosome groups undergoes a second division almost 
immediately, the separated units apparently coming together again 
preceding this division. The dyads of the other group remain huddled 
together in no regular order and no trace of spindle fibres is visible 
(Fig. 7a). In the telophase of the second division there is again a 
dark disc which I have already interpreted as a spindle rest. The 
daughter groups resulting from this division evidently consist of unit 
elements and five of these are found in each group. Already in the 
early telophase, a nuclear wall is formed around one group, whereas 
in the sister group no such wall is at fist visible (Fig. 8a). However, 
slightly later it too forms such a wall, and in both groups the chromo- 
somes rapidly become diffuse (Fig. 9a). 
Of these two nuclei, one now leaves the periphery of the egg 
and advances toward the center where it meets the sperm nucleus. 
The earliest appearance of the sperm in the egg is during the telophase 
of the first maturation division, at which time it still shows the long 
spiral form that is characteristic of sperms found in the ducts of the 
ovary. The sperm head however rapidly loses its outline, swells, and 
becomes spherical (Fig. 7b, Sb and 9b). The two pronuclei, when 
coming together, are frequently of unequal size (Fig. 10b). As if to 
correspond to this inequality, there is in some cases a slight difference 
in the time at which the chromosomes of the fusion nucleus are con- 
densed again prior to the first cleavage division. Thus in Fig. 11, five 
of the ten chromosomes in the first cleavage nucleus are already 
slightly more condensed than the other five, and the two groups retain 
a certain individuality. Possibly it is the eggs which show this feature 
which later giver rise to males, for, as I have pointed out in previous 
papers, the spermatogenesis is characterized by the fact that five of 
the ten chromosomes are evolved in advance of the other five. In the 
present work, however, this point was not definitely settled. 
