496 
Journal of Agricultural Research 
Vol.V, No. 12 
the point of the smaller end to assume the appearance of a nipple-like 
prominence. 
The number of eggs laid by a single individual was not obtained, 
nor were the eggs in the abdomen counted, hundreds having been present. 
Embryonic development 
The average length of the egg stage is 5K days. Individual records 
show that in some cases this may be shortened to 4K days or prolonged 
to more than 6 yi days. From the hundreds of developing eggs exam¬ 
ined it was determined that only one larva hatches from each egg. 
Development progresses rapidly within the egg. At first little can 
be distinguished, except that the egg becomes strongly curved, increases 
in size, and becomes more opaque, owing to the formation of the germ 
band. When the egg is ready to hatch it has increased in size from 
0.09 or 0.10 mm. in length to 0.66 or 0.70 mm., and proportionally in 
width. This great increase in size can possibly be explained by the 
fact that the egg is probably deficient in nutritive matter when laid 
and that this is absorbed from the blood of its host by the developing 
embryo. 
When embryonic development has progressed sufficiently to show the 
form of the embryo, this is seen to be surrounded by a single embryonic 
envelope one cell layer deep which, according to Korschelt and Heider 
(3, p. 287) y 1 is the serosa (PI. L, fig. 1). Whether the amniotic and 
serosal envelopes are at first separate has not been determined. Accord¬ 
ing to Graber's observations on Hymenoptera, as reviewed by Korschelt 
and Heider, it would seem that the two envelopes are separate at first 
but later become indistinguishably united. At the time of hatching, 
a portion of the cells of this so-called serosal envelope are cast out at the 
poles of the egg (PI. L, fig. 2) and become a body of loose cells lying 
between the chorion and the embryo (PI. L, fig. 3), which is now tightly 
inclosed by a layer of broad, flattened cells made up of the remaining cells 
of the envelope (Pi. L, fig. 3). This rapid division apparently indicates 
that this envelope was the product of the fused amnion and serosa, which 
now separate at hatching time, the loose mass of cells being of serosal 
origin and the remaining thin envelope the amnion surrounding the 
embryo. Henneguy (2, p. 336-337), however, discusses insects that have 
only one embryonic envelope and lists among these parasitic forms, vege¬ 
table or animal, of the Cynipidae, Pteromalidae, and probably Ichneu- 
monidae. It will be interesting to note whether other investigators 
observe this splitting of the single embryonic envelope at hatching time. 
The mandibles can be seen forming at an early stage, and their chitini- 
zation can be seen to progress until maturity is reached at hatching time. 
1 Reference is made by number to “Literature cited,” p. 506-507. 
