830 
Journal of Agricultural Research 
Vol. XXVIII, No. 8 
cocoons (PI. 1, E) during April and the early part of May. A group of approx¬ 
imately eight individuals emerge from each host puparium of the Hessian fly 
when parasitized by this insect. The female parasites, whether fertilized or un¬ 
fertilized, deposit their eggs in the eggs of the host (PI. 1, A, B) which are de¬ 
posited on the wheat plants by the spring generation of flies. The parasite eggs 
begin development immediately (PI. 1, C), the embryos being fully formed in 
the nearly mature host larvae (PI. 1, D) by the first of June. During June and 
July the parasite larvae feed upon the contents of the host larvae, each group of 
parasites devouring all of a host larva (PI. 8, C) with the exception of its integu¬ 
ment. After the parasite larvae are fully grown (PI. 8, B) they remain for some 
time in their cocoons which they have prepared inside the host larval integument. 
About the latter part of July the larvae transform to pupae (PI. 8, D), these in 
turn transforming to adult parasites some time during August. 
The adult parasites remain in their cocoons (PI. 1, E) during the winter, being 
protected by the puparium or toughened integument of the host; and emerge 
from their cocoons and the host puparia in spring, by gnawing one or more holes 
through the cuticula and puparium of the host (PI. 1, F). These adult parasites 
then search for eggs of the spring generation of the Hessian fly in which to 
oviposit. 
PRECLEAVAGE DEVELOPMENT OF THE EGG 
The eggs of Platygaster vernalis are always deposited singly, but occasionally 
a second or third egg may be placed in the same host egg by other females. 
However, the same female parasite usually avoids ovipositing in any host egg 
more than once. This parasite differs from Platygaster hiemalis, another parasite 
of the Hessian fly, therefore, in the number of eggs deposited at one time; P. 
hiemalis , as has been shown by the writers (4), placing a cluster of four to 
eight eggs in the host egg at each oviposition. 
The egg of Platygaster vernalis is always so placed in the host egg that it is 
eventually found in the mid-intestine of the host embryo or young larva with 
unfailing regularity (PI. 1, C). The egg does not and apparently can not undergo 
development in any other part of the host. The proper placing of the egg is 
doubtless accomplished by a complete coordination of certain factors, among 
which are the orientation of the host egg, the manner of striding the egg by the 
parasite, and the length of the parasite’s ovipositor. It is of interest to note, on 
the contrary, that P. hiemalis always deposits its eggs in the host egg, so that 
they are never lodged in the mid-intestine, where apparently they would fail to 
develop. 
THE NEWLY DEPOSITED EGG 
The newly deposited egg is somewhat elongate, but it soon becomes more 
compact, cylindrical in shape, and rounded at both ends (PI. 2, A), measuring, 
according to fixed and sectioned material, approximately 21 m in length and 8 m in 
width. The protoplasm of the egg appears very finely granular and uniform, 
and contains a spherical and darkly staining concentrated nucleus which measures 
3 m in diameter. Immediately after oviposition the nucleus is found in or near 
the center of the egg. The long and thread-like sperm (PI. 2, B) is somewhat 
difficult to demonstrate in all eggs deposited by fertilized females, probably 
because of its wavy and spiral position in the protoplasm of the egg. There is 
also some evidence that not all eggs deposited by impregnated females are in¬ 
seminated. The nucleolus or germ-cell determinant is wanting, just as it is in 
Platygaster hiemalis , and in P. dryomyiae as shown by Silvestri ( 8 ). 
