32 
Journal of Agricultural Research 
Vol. XXV, No. I 
An average of 23.89 per cent of the spring generation of the host is 
destroyed annually by Platygaster vernalis throughout this territory. 
This statement is based on the examination of 18,656 puparia collected 
during a period of six years (1915 to 1920, inclusive) from 39 well 
separated localities ranging from Montoursville, Pa., on the north, to 
Staunton, Va., on the south. Table I gives the percentage for each of 
these years and the average for the period. 
DISTRIBUTION 
Platygaster vernalis has been found throughout the eastern wheat¬ 
growing region as far north as 43 0 33' and as far south as 37 0 50' north 
latitude. Considerable material collected at Evans Mills and Theresa, 
N. Y. (a little north of the forty-fourth parallel), revealed no vernalis 
present. No abundance of vernalis was found farther south than Staun¬ 
ton, Va., a short distance north of the thirty-eighth parallel. This 
species was not found in material collected at Lexington, Va., about 35 
miles southwest of Staunton, but one specimen was reared from material 
taken at Buchanan, about 20 miles southwest of Lexington, latitude 
37° 50'. In the Middle West P. vernalis has been found in abundance at 
Wanatah, Ind., and records have been made of its occurrence at Niles, 
Mich., Strongville, Wooster, Troy, and Columbus, Ohio, and Charles¬ 
ton, Mo. 
THE EGG 
The egg is highly refractive, claviform in shape, and before oviposition 
measures about 0.07 millimeter long by 0.016 millimeter wide. (PI. 
1, A, B.) A minute projecting piece of membrane may sometimes be 
found at the swollen extremity. Immediately after oviposition the 
main body of the egg (PI. 1, B) is usually found dilated to about twice 
the width mentioned. Plate 1, A, shows a camera-lucida sketch of an 
egg freshly removed from the ovary, and Plate 1, B, represents an egg 
immediately after it was oviposited into the host egg. 
The egg never develops except in the midintestine of the host. Sur¬ 
rounded by the chyle of the stomach, it is tossed about by peristaltic 
action. Plate 1, C, shows a Hessian fly larva in longitudinal section 
with a single vernalis egg about 22 days old submerged in the chyle in the 
midintestine. 
The germ cell of the egg, instead of developing as a single embryo, as is 
the case with most insects, gives rise to several embryos. The nutritive 
plasm also develops precociously. Plate 1, D, shows a parasite body 
about 11 days old in sagittal section with four embryos in the blastula 
stage of development. Paranuclear masses may be seen scattered 
irregularly about in the surrounding plasm. Plate 1, E, shows a parasite 
body containing eight embryos that are much further advanced. Each 
embryo is surrounded by an individual membrane and the surrounding 
plasm is gelatinous in consistency. Paranuclear masses are still present. 5 
The illustration shows the entire mass somewhat flattened out. In the 
host’s stomach it tends to assume a spherical shape, but its plastic nature 
permits it to be compressed into various shapes by the peristaltic action. 
The number of embryos found to develop from a single egg ranges 
from 2 to 12. 
6 The outlines of the sketch weie made by camera lucida immediately after the embryonic mass had 
been taken from the host body and biought into normal salt solution. Later the embryonic mass was 
stained in picrocarmine to bring out the cell structure, and greater details of the sketch were taken from 
these stained and mounted embryos. 
