34 
Journal of Agricultural Research 
Vo!. XXV, No. r 
transverse orifice, when closed appearing as a somewhat crescent-shaped 
slit and when open forming an oval-shaped aperture. In the process of 
feeding, the superior lip is moved toward and away from the inferior lip by 
strong radiating muscles. The inferior lip is slightly thickened along 
its rim. On each side slightly posterior to the mouth is a small, dis¬ 
tinctly curved mandible. (PI. 2, E.) The mandibles are widely sepa¬ 
rated from each other, distinctly chitinized, and less than half the 
length of the mandible of the primary larva. The average length of 1 o man¬ 
dibles from 10 mature larvae was found to be 0.03 millimeter. Slightly 
caudad of the mandibles is a pair of faintly chitinized maxillae (PI. 2, F), 
which are rather broad at the base and taper slightly to a blunt point. 
The maxillae are slightly longer than the mandibles, with the inner side 
a little shorter than the outer. 
During this stage of the parasite, the remainder of the host is consumed 
as far as the cuticula, which is left to inclose the cocoons that subse¬ 
quently are formed. 
THE COCOON 
The cocoon (PI. 3, A) is broadly ellipsoidal and of a flexible, smooth, 
shiny, yellowish brown consistency. The cuticula of the host is left 
intact, but adheres so tightly to the cocoons as to appear as part of them 
and doubtless serves as a protection to them. In Plate 3, A, the external 
spatula of the host may be seen adhering at one extremity. From 3 to 13 
such cocoons have been found in single hosts, and the examination of 100 
hosts showed an average of 7.91 cocoons per host. The host invariably 
formed its brown puparium case before being killed by the larvae of Platy - 
gaster vernalis , thus providing the hibernating parasites an additional 
protection. 
THE PUPA 
The pupa (PI. 3, B), when first formed within the cocoon, is white, but 
the compound eyes soon darken and gradually the entire body turns a 
shiny black with the exception of the thin integument between the 
abdominal plates. The pupal stage is shorter in duration than either the 
larval or the adult stage. 
THE ADULT 
DISTINGUISHING MORPHOLOGICAL CHARACTERISTICS 
The adult (PI. 4, A) is from 0.7 millimeter to 0.9 millimeter long’ 
with shining black body. Certain distinguishing characteristics are as 
follows: 
Head quadrate, about as wide as thorax; face convex; occiput, vertex, and face dis¬ 
tinctly transversely rugulose (PI. 4, B); antenna with base of scape black, second joint 
of the flagellum in male distinctly curved and larger than that of the female (PI. 4, C 
andD); scutellum laterally margined; legs entirely piceous; tarsi fuscous; wings 25^ to 
3 times as long as abdomen; ovipositor (PI. 3, C and D) straight, slightly enlarged and 
blunt at apex. Plate 3, D, shows the sheath, gorgeret, and stylet of the ovipositor. 
The ovaries are also characteristic of the species, being nearly spherical, with short, 
thick oviduct about as long as the diameter of the ovary. A single ovary is shown 
in Plate 3, E. 
PARTHENOGENESIS 
Experimental rearings have shown that parthenogenesis may occur in 
Platygaster vernalis. In one experiment seven unfertilized females were 
put under a cloth-topped glass cylinder on potted wheat plants bearing 
eggs of the Hessian fly on their leaves. The Hessian fly larvae which 
