1194 
Journal of Agricultural Research 
Vol. XXVIII, No. 12 
to the dorsal body wall of each side along the suture separating the prescutum 
from the scuto-scutellum and in fact determining this sutural line. 
In the thoracic region (fig. 4, A) the musculature is slightly different from 
that of the abdomen. The ventral longitudinal and oblique muscles (' VLMcl ,. 
VOMcl ) are readily recognized, although here their lateral extent is reduced, 
especially in the prothorax. The dorsal longitudinal muscles ( DLMcl ) are 
present in all three thoracic segments. In the prothorax there are present two 
groups of dorsal oblique muscles whose arrangement may be gathered from the 
figure. In the mesothorax and metathorax the dorsal oblique muscles are divided 
into two parallel groups. A strong muscle (2LOMd) crosses the lateral face of 
each of the three segments, running from its posterior border cephalad and 
dorsad to its anterior border. This muscle is absent in the abdominal region. 
In the meso- and metathorax a very large muscle ( lLOMcl ) is attached by a 
broad line of attachment to the ventral side of the segment, mesiad of the leg 
rudiments ( 1 L~SL) , and runs laterad and caudad to the posterior margin of the 
segment near the lateral margin of the area occupied by the dorsal longitudinal 
muscles. This muscle evidently corresponds to the major oblique muscles of 
the abdomen. In all three thoracic segments the minor lateral oblique muscles 
(; 2LOMd) connect the anterior and posterior margins of their respective seg¬ 
ments, crossing the lateral body wall in an oblique direction. It seems doubtful 
whether these muscles are truly homologous with the minor lateral oblique 
muscles of the abdominal segments. In the mesothorax and metathorax a dorso- 
ventral muscle spans the imaginal wing disks. This muscle is much larger in 
the pro thorax than in the metathorax. 
The effects of the contraction of the various trunk muscles may be inferred 
from their size, direction, and attachments. These effects may readily be seen, 
however, on the external surface of the larva. If the figure showing the external 
features of the larva (PI. 1, D) be compared with figure 4, B, it will readily 
become evident that the superficial contour of the larva is determined principally, 
if not exclusively, by the trunk muscles. The evident division of the trunk into 
segments is not, as in the imago, due to the formation of sclerites, but is produced 
principally by the longitudinal trunk muscles, aided, of course, by the ventral 
oblique, the major lateral oblique, and the smaller dorso-ventral muscles. The 
epipleural lobes are referable to the action of the major oblique muscles, the 
sharp demarcation of these lobes from the sternal area being apparently due to 
a certain amount of rigidity imparted to the body wall in this region by the ventral 
longitudinal and oblique muscles, since the area occupied by these coincides 
with this area. The depressions in which the spiracles are located are produced 
by the action of the minor lateral oblique muscles, aided, of course, by the 
posterior set of dorso-ventral muscles. The sutural lines obliquely traversing 
the dorso-lateral surface of the segments are plainly to be identified with the 
anterior insertions of the dorsal oblique muscles. 
Detailed accounts of the muscular systems of hymenopterous larvae are 
lacking. The account by Carrikre and Burger (7) of the muscular system of 
the mason bee and that by Anglas ( 1 ) of the muscular systems of Vespa and the 
honeybee are extremely brief. Both merely recognize dorsal and ventral longi¬ 
tudinal muscles, and a set of obliquely arranged dorso-ventral muscles. An 
examination of the accounts of the muscular systems of the larvae of other 
orders, such as that recently given by Forbes (10) for lepidopterous larvae, dis¬ 
closes no basis for comparison with the bee larva. The muscles of the latter 
are, in comparison, few and simple, as might be inferred from its mode of life. 
Anglas ( 1 ) states that some of the larval muscles, more particularly those of 
the abdomen, persist with slight modification through nymphosis into the imago. 
A study of the muscles of the abdomen of the imago shows them to be so different 
