338 
Journal of Agricultural Research 
Vol. XXV, No. 8 
The early development of the parasite takes place in the host egg and 
in the young host larva during fall (PI. i, C, E), the winter being passed 
in the embryonic stage within a well developed host larva, which remains 
on the wheat plant. In spring the Hessian fly larvae, if unparasitized, 
soon produce adult flies. Meanwhile, the parasites in parasitized host 
larvae complete the embryonic stage of development, and remain in this 
condition in the fully grown host larvae until early summer. During 
July the newly developed parasite larvae mature by feeding upon the 
body content of the host. The parasite larvae then pupate in individual 
cocoons made within the host puparium, the adult parasites finally 
emerging from their cocoons in the fall. 
DEVELOPMENT OF THE EGG TO CLEAVAGE 
The precleavage development of the egg of but one species of the 
Platygastridae (Platygaster dryomyiae Silv.) which develops by the 
monembryonic method has been described by Silvestri (u). 6 This 
phase of the development of polyembryonic Hymenoptera has been 
demonstrated by Silvestri (9) and Patterson (5) in Copidosoma trun - 
catellum and by Leiby (2) in Copidosoma gelechiae. In all cases it has 
been shown (1) that two maturations of the oocyte nucleus occur, (2) 
that the two resulting polar bodies are not thrown off (a 3 they usually 
are in monembryonically developing eggs) but are retained in the anterior 
or polar region of the egg, (3) that the polar region is differentiated 
from the posterior or embryonic region, and forms together with the 
polar bodies a nucleated membrane which encompasses each embryo in 
the course of its development, and (4) that the fertilized or unfertilized 
cleavage nucleus divides and is destined eventually to give rise to the 
embryos. The processes by which the precleavage stages of these eggs 
take place differ only slightly, but the later stages of development of 
the demonstrated species are known to differ very markedly. 
THE NEWLY DEPOSITED EGG 
The eggs of Platygaster hiemalis are regularly deposited in groups of 
from 4 to 8, at each oviposition in the host egg. Hence they are fre¬ 
quently found in contact and side by side (PI. 1, A), or very close to each 
other. It, therefore, is not difficult to ascertain whether a host egg has 
been oviposited in more than one time, or how many eggs are deposited 
at a single oviposition. 
The newly deposited egg (PI. 1, E) is ovoid in shape, usually bluntly 
rounded at the posterior end, and somewhat pointed at the anterior end. 
Sectioned eggs measure 15/x in length and 6/4 in width, or 5/1 in length 
and 2/4 in width less than freshly deposited unfixed eggs. The cytoplasm 
of the egg is densely and finely granular, homogeneous throughout, and 
without oil spherules or vacuoles. The presence of a wealdy defined 
membrane or chorion becomes evident in eggs that shrink considerably 
following some fixations. 
The egg nucleus is spherical and measures 2.5/4 in diameter. It is 
regularly found in or very near the center of the egg. When sectioned 
the nucleus of the newly deposited egg exhibits its chromosomes scattered 
over a reticulum. 
•Reference is made by number (italic) to "Literature cited," p. 349. 
