May 24,1924 Polyembryonic Development of Platygaster vernalis 
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MATURATION AND THE ORIGIN OF THE PARANUCLEAR MASSES 
In a general way the maturation of the egg of Platygaster vernalis is similar 
to that described for other species of Platygaster. As far as can be ascertained, 
it is identical in fertilized and unfertilized eggs. As in previously described 
polyembryonic and some monembryonic Hymenoptera, the polar bodies ar 
retained in the egg and eventually give rise to the paranuclear masses which 
have a nutritive function in the course of development of the embryos; while 
the oocyte nucleus, whether fertilized or not, gives rise to the embryos. 
The first maturation of the oocyte nucleus is completed during the first eight 
hours after oviposition. Within the first 30 minutes the nucleus begins to expand, 
and by the fifth hour it is in the prophase stage of mitosis (PL 2, B, C). There¬ 
after maturation is completed quickly; the chromosomes being found first, 
grouped together at each end of the spindle but distinct from each other (PI. 2, 
D), and then, later, somewhat concentrated into two separate nuclei (PI. 2, E). 
The chromosomes of each of thejtwo nuclei then condense further and form 
irregularly shaped, homogeneous, dark staining nuclei (PI. 2, F, G), which are 
always quite conspicuous in the egg in spite of their small size. The first matura¬ 
tion takes place longitudinally in thejanterior half of the egg, and results in the 
production of the first polar body, which passes to the anterior edge of the egg, 
and the oocyte nucleus of the second order, which remains near the center of the 
egg. 
Between the eighth and the^twelfth hours after oviposition the first polar body 
and the oocyte nucleus of the second order remain quiescent, but about the 
twelfth hour a second maturation of the oocyte nucleus commences, and the 
mitotic division results in the production of two distinct groups of chromatin 
material in the central region of the egg (PL 2, H-J). The second maturation 
spindle is always considerably shorter than the first. Various stages of the 
division can be observed in eggs that are 12 hours old, indicating that second 
maturation is completed quickly. The anterior of the two centrally-disposed 
nuclei is the second polar body, which later migrates toward the polar or anterior 
region of the egg by the side of the first polar body. The posterior nucleus of the 
second maturation spindle becomes the female pronucleus of the fertilized egg or 
the cleavage nucleus of the unfertilized egg. It remains in the posterior half of 
the egg from the twelfth to the twenty-fourth hour, increasing in size during this 
interval from a diameter of 2.2 y just after maturation is completed to 5.4 y at 
the time of fusion with the male pronucleus. 
About 24 hours after oviposition the two polar bodies begin to expand, 
becoming at first spherical and then oval (Pl. 2, K, L; Pl. 3, A, B), thus assuming 
the shape and appearance of typical paranuclear masses, as described for other 
polyembryonic Hymenoptera. As the polar bodies expand the chromatin breaks 
up into numerous small granules which are scattered throughout the plasm of 
each nucleus. As will be shown later, the polar bodies (henceforth known as 
paranuclear masses) migrate about in the egg and divide amitotically into similar 
secondary masses. J| It should be noted that simultaneously with the expansion 
of the polar bodies the egg increases in size, measuring in its greatest diameter 
when 1 day old approximately 28 y in length and 9 y in width. 
FERTILIZATION 
During the first six hours after oviposition the sperm transforms into an oval 
nucleus (Pl. 2, D, E), which is always located in the posterior region of the egg. 
A stage of the male nucleus is then evident, when the chromatin resembles a 
tightly coiled thread (Pl. 2, F). The threadlike chromatin next breaks up into 
