DEVELOPMENT. 17 
a rosy tint. It presents a very delicate appearance, the pupal 
being extremely thin. On the front is a prominent pointed chitinous 
rostrum of a brown color, the function of which is considered to be the 
cutting of the puparium to permit the exclusion of the papa. Above 
the origin of the antenme are two horns called by M arena] the cephalic 
horns and posterior to them two larger, curved, thoracic horns (Plate 
II C.) which contain, according to Marchal, trunks of the tracheal y 
system. 
DEVELOPMENT. 
The deposition of the eggs has been described with great care by 
Herrick (50), as follows: 
The eggs are laid in the long creases or furrows «>f the upper surface of the haves 
of the young wheat plant. While depositing her eggs, the insert stands with her 
head toward the point or extremity of the leaf, and ar various distances between 
the point and where the leaf joins and surrounds the stalk. The number found on 
a Bingle leaf varies from a single eg^ up to thirty or even more. The egg is about a 
fiftieth of an inch long, cylindrical, rounded at the ends, glossy and translucent, of 
a pale-red color, becoming in a few hours irregularly spotted with deeper red. 
Between its exclusion and its hatching, these red spots are continually changing in 
number, size, and position; and somtimes nearly all di>appear. A little while before 
hatching, two lateral rows of opaque white spots, about ten in number, can be M-en 
in ea<h egg. In four days, more or less, according to the weather, the egg is hatched. 
On the hatching of the larva and during its first or locornotory stage 
as defined by Marchal it moves down the leaf and along within the 
leaf sheaf until it reaches a position near the base of the culm. This 
in the case of fall wheat is close to the root and at or beneath the sur- 
face of the soil. In the case of spring wheat, when the eggs are usually 
placed on leaves above the first joint, they are just above the first or 
it may be the second joint ; very rarely higher on the stalk. 
Having reached this position the larva changes probably by a true 
moult to the second larval form, which is a sedentary feeding form 
during which there is no movement from the point where it has located, 
but has a fixed feeding period during which it secures ail the material 
for its growth. At the end of this Btage, which lasts on an average 
about twenty days, the larva contracts, and the outer larval skin forms 
a puparium, or sheath, within which the larva changes to the third 
larval form. In this retention of the larval skin as a protecting case 
the Hessian fly differs from most of the Cecidomyidae and agrees with 
the more specialized flies of tin- house-fly group, and it would seem 
that this adaptation is one which lias come with the peculiar restric- 
tions of the species and the necessity it has encountered of adapting 
itself to varying climatic conditions. 
While the third larval form is apparently a quiescent one and cer- 
tainly one which is found capable of great modification in time, it 
really embraces some most important steps of development. While no 
nutriment is taken there is an important change in the tissue elements — 
the growth of histoblasts from which arise the rudiments of the 
6086— No. lb 2 
