A. J. (tROVE 
471 
V. The Musculature of the Setae ( PL XXVI, figs. 2-7). 
(a) The \protractor muscles of the mandibles. Each mandibular seta is pro¬ 
vided with two protractor muscles, one of which is attached to the inner face 
of the base of the seta, and the other to the outer face. Suitable points' of 
attachment to the seta for the muscles are provided by flange-like prolonga¬ 
tions of the chitin of the base of the seta. At its lower end the inner muscle 
becomes continuous with the inner face of the maxillary sclerite and the outer 
muscle to its outer face. Of the two muscles, the inner one is shorter and less 
powerful than the outer. At their point of attachment to the mandible, the 
protractor muscles almost surround the base so that, in transverse sections, 
the seta appears to be embedded in muscle (PI. XXVI, fig. 3). 
( b ) The protractor muscles of the maxillary setae. Like the mandibles, each 
maxillary seta is provided with two protractor muscles, but they lie close 
together and are attached to the outer face only of the base of the seta. Also 
the muscles are not so large as is the case with the mandibles. At their setal 
end, the muscles are attached to the outer side of the base of the seta, and 
t 
special flange-like prolongations of the chitin do not appear to be present to 
serve as points of attachment. At their lower ends the muscles are joined on 
to the inner face of the maxillary sclerite. 
With both mandibular and maxillary setae, the effect produced by the 
contraction of the protractor muscles will be to pull the bases of the setae 
towards the buccal region. 
(c) The retractor muscles of the mandibles. These muscles, of which each 
mandible has two, are attached to the base of the seta at the opposite side of 
the inner face of the flange which serves as a point of attachment for the inner 
protractor muscle. The two muscles are large, lie closely together, and stretch 
upwards in the head towards the under side of the anterior support of the 
transverse bar, to the clypeal half of which they are attached. The muscles 
are relatively longer and more powerful than the protractor muscles. 
(d) The retractor muscles of the maxillary setae. Each maxillary seta has 
two retractor muscles, but these are very closely applied to one another, so 
that in section they appear almost as a single muscle, but the dividing line 
between them remains clear. The muscles stretch from the inner face of the 
base of the seta to the under side of the anterior support of the transverse bar, 
but are attached nearer to the transverse bar than is the case with the re¬ 
tractor muscles of the mandibles. 
When the retractor muscles of the mandibles and maxillary setae contract, 
they will tend to draw the bases of the setae further into the head. 
VI. The Muscles of the Head Capsule and, Neck. 
In addition to the muscles already enumerated, there are a number of 
muscles attached to the various sclerites composing the head. They are- 
arranged in groups, and are indicated briefly in the order in which they appear 
in a series of transverse sections of the insect. 
