Aug. as, 1933 
Twinning and Monembryony in Platygaster hiemalis 339 
If the egg is inseminated the sperm can be seen usually in a curved or 
arched position (PI. 1, E; PI. 2, A~C), and frequently extending more 
than two-thirds the length of the egg. The body part and tail of the 
sperm measure 2.7^ and 7.3/1, respectively. Never more than one sperm 
has been found in one egg. It is quite evident that not all of the eggs 
deposited at one time by a fertilized parasite contain sperms. This 
point has been studied thoroughly, careful examinations of groups of 
eggs showing that about one-third of the eggs are not inseminated. 
For example, only 5 of the group of 8 eggs shown at F on Plate 1 contain 
sperms. 
There is no evidence whatever of the presence of a nucleolus or so-called 
germ-cell determinant. Nor did Silvestri find this nuclear body in 
Platygaster dryomyiae , although it has been recorded as present in the 
eggs of polyembryonic Hymenoptera previously described. 
maturation 
Both fertilized and unfertilized eggs maturate and develop adult 
parasites, the fertilized eggs presumably giving rise to females and the 
unfertilized eggs developing males; although on this point no conclusive 
biological or cytological evidence is available. The process of matura¬ 
tion is identical in fertilized and unfertilized eggs. 
During the first hour after oviposition the oocyte nucleus (PI. 1, E; 
PI. 2, A) increases slightly in size and becomes clearer, whereupon the 
chromosomes are seen scattered over a reticulum. The nucleus then 
becomes more concentrated (PI. 2, B) and is found immersed in a semi- 
clear area of the oocyte cytoplasm. During this time its chromatin 
appears as a condensed mass of fine granules. Two hours after oviposi¬ 
tion the nucleus again expands slightly (PI. 2, C) and chromatin bodies 
are to be seen supported at the nodes of the reticulum. At four hours 
the nucleus is found at prophase, in the act of forming a spindle, or at 
anaphase (PI. 2, D-F). The spindle is always arranged longitudinally 
in the egg. At the close of the first maturation the first polar body is 
always found at the anterior pole while the oocyte nucleus of the second 
order is found near the center of the egg (PI. 2, G). 
Previous to the second maturation, which takes place at about the 
seventh hour, the first polar body becomes concentrated and appears 
as an irregular homogeneous mass of chromatin that measures about 
i/z in diameter. Between the fourth and the seventh hours, the oocyte 
nucleus of the second order undergoes changes similar to those described 
for the nucleus previous to the first maturation; and at the end of the 
seventh hour the nucleus is found at prophase (PI. 2, J). The spindle 
which is then formed is again disposed longitudinally in the anterior 
half of the egg (PI. 2, D, M). 
After the second division, the second polar body is seen in the an¬ 
terior end, near or adjacent to the first polar body; while the oocyte 
nucleus of the third order (later the female pronucleus) remains in the 
center of the egg until about the ninth hour, after which it may be found 
almost anywhere in the posterior half of the egg. From the eighth to 
the sixteenth hour the female pronucleus is apparently in a resting stage, 
although during this interval it increases in diameter from 1.8 pi to 3.5 pt. 
