684 LaurA FLORENCE 
double origin, one branch originating in the dorsal wall of the head and 
the other in the chitinous cuticula between the head and the thorax. 
After the fusion of the two branches each muscle passes ventrad and 
slightly forward to the level of the floor of the sheath, where they bend 
at a rather sharp angle and pass a little way backward to their insertion in 
the floor of the sheath under the anterior ends of the rami (Plate LX, 6). 
The ventral muscles are two stout strands originating in the ventral wall 
of the neck and passing forward under the sheath almost to the angle 
of its posterior retractors, when they bend sharply back on themselves. 
Each muscle almost immediately divides into two slender strands, which 
are inserted in the posterior ends of the rami of the elements of the ventral 
piercer. They are the retractors of the ventral element of the piercers. 
The dorsal muscles lie on the dorso-lateral wall of the sheath and are the 
retractors of the dorsal element of the piercers. They originate in the 
posterior chitinous cuticula between the head and the thorax, and lie 
doubled on themselves just as do the retractors of the ventral element of 
the piercers. They are inserted in the posterior ends of the rami of the 
dorsal element of the piercers. The lateral posterior retractors control 
the sheath and the piercers, while the dorsal and ventral posterior retractors 
control the movements of the separate elements of the piercers. The 
contraction of the lateral retractors of the sheath brings its anterior part 
to a resting position, and the simultaneous contraction of the posterior 
retractors begins the withdrawal of the mouth parts from the wound. 
They come to their final resting position through the relaxation of the 
protractor muscles and the consequent straightening, through its own 
elasticity, of the plate imbedded in the floor of the sheath. 
The true relationship between the pharynx and the sheath and mouth 
' parts can be fully understood only if the study of serial sections supplement 
that of gross dissections and mounts in toto. In a section through the 
head at the anterior level of the attachment of the basal part of the 
““mandibles”’ of Enderlein to the lateral wall of the head, the two halves 
of the dorsal piercer are seen lying tubelike close under the dorsal wall 
of the buccal plate and are here more strongly chitinized than elsewhere. 
Beneath it lies the ventral element of the piercers, with the salivary duct 
in its canal (Plate LXI, 1). The pumping pharyngeal tube does not reach 
this far forward when in its resting position. From the ventral wall of 
the buccal plate two outgrowths are continued ventrad as a chitinous 
