June 21 ,1921 Morphology of the Honeybee Larva, 1191 
to an insertion on the ventro-lateral surface of the head, just caudad of the base 
of the maxilla (PI. 6, C, EMx). It apparently serves to rotate the maxilla 
outward. 
labium 
The labium is provided with two pairs of retractors. The larger or major 
retractors (Pl. 6, C, IRLb) take their origin from the neck fold just ventrad of the 
external ends of the transverse arms of the tentorium. From there they run 
cephalad, converging meanwhile, and are inserted, a short distance apart on 
either side of the ventral mid-line, on the posterior margin of the labium. These 
muscles by their contraction withdraw the labium into the ventral part of the 
head. The minor retractors (PI. 6, C, 8RLb) are slender muscles which have 
their origin directly cephalad of the insertions of the major retractors. From 
here they run cephalad, converging at the same angle as the major retractors, 
to the tip of the labium where they are inserted on the wall of the common duct 
of the silk gland. These muscles serve to retract the tip of the labium. The 
two sets of retractors, when seen from the ventral surface, form a figure resembl¬ 
ing the letter Y, inverted. 
LABRUM 
At the base of the clypeus is a pair of well defined muscles (PL 2, B, and 6, C, 
ClpMcl ), each of which takes its origin from the head capsule at the dorsal margin 
of the line of junction with the anterior arms of the tentorium. From these 
points the two muscles pass dorsad and slightly mesiad to insertions on minute 
apodemes on the dorsal wall of the head capsule, near the mid-line, at the base 
of the clypeus. These insertions are marked on the exterior by shallow depres¬ 
sions of the surface (see PL 1, F). Immediately cephalad of the insertions of 
these muscles, a second pair of muscles, the retractors of the labrum (Pl. 3, A, 
and 6, C, RLm ), have their origin. These are inserted on the posterior edge of 
the clypeus in the dorsal mid-line. 
Certain other muscles located in the labrum and clypeus and associated with 
the pharynx are described in the section on the alimentary canal (see p. 1184). 
CRANIAL MUSCLES 
Two other pairs of muscles are found in the head which pass from the tentorium 
to the cranial wall. The muscles of the first pair are slender, and originate on 
the dorsal surface of the anterior arms of the tentorium, near the junction of 
the latter with the transverse bar. These two muscles then pass dorsad on either 
side of the oesophagus, between the two halves of the brain, and are inserted on 
the median fold of the dorsal cranial wall. It is worthy of note that in prepara¬ 
tions of larvae which have completed their growth these muscles appear to have 
lost their attachment to the dorsal cranial wall. This change is presumably 
related in some way to the approaching metamorphosis. The muscles of the 
second pair are also well developed in young larvae, but insignificant in older 
ones. Each of these muscles takes its origin from a long spur on the dorsolat¬ 
eral face of each of the anterior arms of the tentorium (Pl. 1, A, ApTeri). 
These spurs are directed dorsad and laterad. In the young larvae the muscle 
fibers are directed dorsad and laterad, diverging meanwhile, and have broad 
insertions on the lateral walls of the head capsule, laterad of the cerebral lobes 
(36). In old larvae the spurs are long and directed cephalad and dorsad, extend¬ 
ing nearly to the anterior cranial wall (Pl. 6, D), the short gap being bridged by a 
few muscle fibers inserted on the anterior wall of the cranium just dorsad of the 
antennal rudiments. The points of insertion are marked externally by well- 
defined circular depressions (see Pl. 1, F). Kirmayer (86) finds similar spurs on 
the tentorium and corresponding muscles in the]head of the Yespa larva. 
