832 
Journal of Agricultural Research 
Vol XXVIII, No. 8 
numerous pieces (PL 2,1), which are then distributed over a matrix (PL 2, G, H). 
Meanwhile, the nucleus has expanded until it measures approximately 5 m in 
diameter. These changes undergone by the male nucleus are not always syn¬ 
chronous with the various stages of maturation but they take place between the 
tenth and twelfth hours after oviposition. From the twelfth to the twenty- 
fourth hours the male nucleus remains in a quiescent condition. 
Fusion of the male and female pronuclei is effected about 24 hours after ovipo¬ 
sition, in the posterior half of the egg (Pl. 2, K, L; Pl. 3, A, B). The egg now 
contains two paranuclear masses in its anterior region, and a cleavage or embry¬ 
onic nucleus in its posterior region. 
DIFFERENTIATION OF TROPHAMNION AND EMBRYONIC REGION 
Shortly after the cleavage nucleus is formed, an area is seen to encompass it 
which is somewhat less dense than the remainder Qf the egg. This more lightly 
stained area is the embryonic region (Pl, 3, B), which together with the cleavage 
nucleus gives rise to the embryos. The remainder of the egg containing the two 
paranuclear masses constitutes the trophamnion. 
The egg is henceforth properly known as the parasite body, for it now begins 
to increase in size. The active feeding of the host, which is soon to commence, 
permits the trophamnion to absorb the elements from the chyle in the host which 
are necessary for further growth. Similarly, the elaboration of the trophamnion 
and the distribution of the paranuclear masses within it are conducive to cleavage 
and the development of the embryos. 
SUMMARY AND DISCUSSION OF PRECLEAVAGE DEVELOPMENT 
In most respects the precleavage development of Platygaster vernalis is not 
unlike that previously described by the writers ( 4 ) for P. hiemalis y nor even greatly 
different from that described by Silvestri (8) for P. dryomyiae, which develops 
monembryonically. In P. dryomyiae the first polar body divides during the 
second maturation of the oocyte nucleus, and the second polar body, produced 
at second maturation, unites with the posterior half of the divided first polar 
body to form one paranuclear mass; while a second paranuclear mass is developed 
from the anterior half of the divided first polar body. In P. hiemalis the writers 
have shown that the two polar bodies, resulting from the two maturations of the 
oocyte nucleus, unite to form one polar nucleus, which later divides to form two 
subequal paranuclear masses. It has been shown above that in P. vernalis the 
two polar bodies neither divide (as they do in P. dryomyiae ), nor unite (as in P. 
hiemalis ), but that they develop directly by expansion into two subequal para¬ 
nuclear masses. 
If there is any significance in the fact that the first polar body divides before 
forming a paranuclear mass, or that the two polar bodies coalesce, or that they 
develop directly into paranuclear masses, it is not yet understood. In any event, 
the object accomplished is identical: paranuclear masses originate from the polar 
bodies, and are confined thereafter to a differentiated plasm of the egg known as 
the trophamnion. The function of the trophamnion is nutritive. It elaborates 
as the parasite body grows, and portions of it eventually surround each embryo 
of a polyembryonal mass, thus permitting each embryo to be so nursed that it 
can develop into a young larva. Henceforth the insect is able to provide for 
itself by direct feeding upon the host. 
In other poly embryonic hymenopters Lei by (8) and the writers (4) have shown 
that the egg, before cleavage or very shortly thereafter, must be encompassed by 
host tissue in order to continue development. Eggs which are not so provided 
