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 thej^ 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 chitinizod 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 



