1206 
Journal of Agricultural Research 
Vol. XXVIII, No. 12 
division into an outer and cortical zone of ganglion cells surrounding an inner 
central core of nerve fibers (punk-substanz). Among the ganglion cells large 
actively dividing neuroblasts, like those of embryos, may frequently be recognized. 
An outer neurilemma is always distinguishable; an inner neurilemma is probably 
also constantly present, but less evident. In the brain of the larva many of the 
typical features of the imaginal brain may be readily recognized, such as the 
arrangement of the cells of the optic lobes to form inner, middle and outer fibrillar 
masses, and the presence of well-developed mushroom bodies. 
(5) The corpora allata are spherical bodies about 0.85 mm. in diameter, 
situated one on each side of the mid-line, close behind the brain, lying on the 
dorsal side of the anterior arms of the tentorium, and in close contact with the 
walls of the aorta. Each is composed of a compact mass of polyhedral cells. 
Tracheoles may be seen to enter these bodies and penetrate between their com¬ 
ponent cells. 
(6) There are ten pairs of spiracles, following the rule for insect larvae, located 
on the 2d and 3d thoracic and the first eight abdominal segments. The spiracles 
of each side open by short branches into a longitudinal trunk. The two trunks 
are united anteriorly by a loop or commissure in the region of the neck, above 
the oesophagus, and posteriorly by a similar loop below the hind-intestine. The 
longitudinal trunks are also connected by segmentally arranged commissures 
which run close to the ventral body wall. Two pairs of tracheal branches from 
the anterior tracheal loop supply the brain, antennal rudiments and other parts 
of the head. Segmentally arranged branches springing from the longitudinal 
tracheal trunks supply the muscles, heart and viscera. The tracheae terminate 
in typical tracheal end cells from which arise the tracheoles. The latter never 
branch or anastomose and have never been observed to penetrate the cytoplasm 
of other cells. 
(7) The alimentary canal comprises a short and relatively slender fore-intes¬ 
tine, a large cylindrical mid-intestine and a hind-intestine. The fore-intestine 
includes mouth, pharynx and oesophagus, these three divisions being somewhat 
ill-defined. The mouth is a wide transverse slit passing immediately into the 
pharynx. The latter is provided with a well-developed epipharynx which con¬ 
sists essentially of a fold of the dorsal wall of the pharynx, and which is provided 
with numerous transversely arranged muscles uniting the lateral margins of the 
fold and also with levator muscles which are attached at the dorsal ends to the 
dorsal wall of the clypeus and labrum. In addition, the pharynx itself is pro¬ 
vided with two sets of dilator muscles and a pair of levators. The pharynx leads 
directly into the tubular oesophagus, which opens into the anterior end of the 
mid-intestine. Here the wall of the oesophagus is reflected upon itself to form 
a fold which projects into the anterior end of the mid-intestine, thus constituting 
an oesophageal valve similar to that found in many other insects. The oesopha¬ 
gus is provided with a muscular coat composed mainly of transverse fibers. 
The mid-intestine is very capacious, cylindrical in form, about one-third of the 
diameter of the body and extends from the prothoracic to the 9th abdominal 
segment. Its walls are thick and composed of large cubical cells displaying the 
usual striated border. A peritrophic membrane, apparently gelatinous in con¬ 
sistency, lines the mid-intestine. This layer appears to be secreted by those 
cells of the mid-intestine lying next to the oesophageal valve. The mid-intestine 
possesses a muscular coat composed of an inner layer of delicate longitudinal 
fibers and an outer layer of transverse fibers. The muscle fibers of both layers 
are branched and anastomose with one another. This is more conspicuously 
seen, however, in the case of the inner longitudinal layer. The posterior end of 
the mid-intestine is completely closed and its extremity is not covered by the 
muscular coat. The hind-intestine is a relatively slender tube, doubled on itself 
