1180 
Journal of Agricultural Research 
Vol. XXVIII, No. 12 
SpBr), to the tracheal trunk (fig. 2, A, TraTr) of the corresponding side. Each 
of these trunks traverses the body cavity, about midway between the hypodermis 
and mid-intestine, slightly ventrad to the line formed by the spiracles of that 
side. The tracheal trunk of a mature larva has an inside diameter of about 0.1 
mm. in its posterior and larger half; in the three anterior segments its diameter 
is reduced to about one-half of this caliber. The anterior ends of the tracheal 
trunks of opposite sides meet to form a loop, the anterior transverse commissure 
(fig. 2, A and B, ATral), in the region of the neck and above the oesophagus; 
a similar loop, the posterior transverse commissure (fig. 2, A, PTraL), is formed 
by the posterior ends of the tracheal trunks. This latter, however, is situated 
ventrad of the posterior end of the mid-intestine, near its junction with the 
hind intestine. The two tracheal trunks are also united by a segmentally 
arranged series of transverse commissures, which lie in the ventral half of the 
body cavity, close to the body wall, passing below the ventral nerve cord. In a 
larva three days old or more the prothorax is seen (fig. 2, A) to possess one com. 
missure, while the mesothoracic, metathoracic, and first abdominal (propodeal) 
segments each possess two commissures. These, however, become confluent 
just before their junction with the tracheal trunks. It should be noted that the 
commissures in the thoracic segments are quite slender, while those in the 1st 
abdominal segment approximate the diameter of the tracheal trunks at this 
point. In the 2d to the 8th abdominal segments the transverse commissures 
are single and of large diameter, the most anterior being largest, while the trans¬ 
verse commissure of the 9th abdominal segment is relatively slender and its 
course somewhat oblique. The prothoracic commissure joins the tracheal trunks 
just in front of the branches from the mesothoracic spiracles, those of the meso- 
thorax just behind these branches. The commissures of the other segments, 
except that of the 9th segment, join the tracheal trunks either close to or slightly 
caudad to the corresponding spiracular branches. 
Throughout their length the tracheal trunks give off numerous branches 
which supply the various regions of the body. Three branches on each side 
supply the head. The more anterior of these (fig. 2, B, Bral) arises from the 
anterior transverse commissure close to the mid-line and runs cephalad to the 
brain, passing beneath the base of the optic lobes. It then turns abruptly 
dorsad, and supplies the anterior face of the brain and the region immediately 
adjacent (a). In the latter part of its course it passes close to and in contact 
with the spine, which arises from the anterior arm of the tentorium on each side. 
The second branch ( Bra2 ) is much larger and arises from the anterior face of 
the transverse commissure a short distance ectad of the branch just described. 
Near its base it gives off a secondary branch ( b ) which passes mesiad and cephalad 
above the brain between the two halves of the protocerebrum, and supplies the 
aorta and the brain in the region of the mushroom bodies. The main branch 
takes a straight course cephalad and slightly ventrad, below the optic lobe, to 
the anterior region of the head, where it divides into three secondary branches. 
One of these (c) curves abruptly dorsad and breaks up into a large number of 
tracheoles at the base of the antennal rudiment. Before terminating its course, 
however, it gives off a twig to the mandible and one to the la-brum. The second 
secondary branch passes mesiad to the head cavity underlying the supraoeso- 
phageal ganglion. The third secondary branch ( d) supplies the maxilla. 
In the prothorax the only tracheal branch worth noting is one (fig. 2, B, e) 
which arises on each side from the single tracheal commissure of this segment 
near its junction with the tracheal trunk, and passes mesiad and cephalad to 
supply the walls of the salivary glands in the region of the neck. In the remain¬ 
ing trunk segments, exclusive of the 9th and 10th abdominal, the number and 
arrangement of the tracheal branches is virtually identical. Springing from the 
