NO. 3 INSECT HEAD SNODGRASS III 



on the anterior dorsal arms (y) of the bars must effect a movement 

 of the hypopharynx, and that the latter would be lifted and swung 

 forward beneath the mouth opening. The pull of the mouth muscles, 

 however, also retracts the mouth angles, and there is probably thus 

 accomplished a closing of the mouth upon the food mass accumulated 

 in the preoral space above the anterior end of the hypopharynx. In 

 the grasshopper, the mouth is closed also by the opening of the jaws, 

 but, so far as can be observed in a dead specimen, the closing of the 

 mouth in this case results mechanically from the transverse stretch- 

 ing of the oral aperture between the separating bases of the adductor 

 apodemes of the mandibles. 



Posteriorly the hypopharynx is fixed to the base of the labium, where 

 its wall is reflected into that of the latter (fig. 41). The hypopharynx, 

 therefore, can swing forward only in unison with the labium, but other- 

 wise it is free to move to the extent permitted by the membranous 

 areas laterad of its base. The only muscles properly belonging to the 

 hypopharynx are the following: 



32. — Retractors of the hypopharynx (figs. 40D, 41) — A pair of 

 muscles arising posteriorly on extreme lateral ends of anterior arms 

 of tentorium (fig. 40 D) ; inserted on posterior parts of basal rods of 

 hypopharynx (fig. 41). 



The contraction of these muscles probably retracts the hypopharynx, 

 and pulls the hypopharynx and labium posteriorly. The mouth aper- 

 ture is opened by the contraction of the dilator muscles inserted on 

 its anterior and posterior walls (figs. 41, 44, JJ, 34, 41). 



The rods {HS) of the suspensory apparatus of the hypopharynx 

 in the grasshopper are evidently remnants of the much larger sus- 

 pensory plates of the hypopharynx in Apterygota and Myriapoda 

 (fig. 21 A, B, C, E, HS). In Microcentrum, as already shown (fig. 

 20 D), a small hypopharyngeal adductor muscle of the mandible is 

 attached to the end of each rod. In the roach (Periplancta) the chi- 

 tinous parts of the hypopharyngeal suspensorium are more strongly 

 developed than in the grasshopper, and their action can be more clearly 

 demonstrated. In the bees, though the hypopharynx itself may be 

 lacking, the oral arms of the suspensory bars are prolonged as slender 

 rods into the lateral walls of the pharynx, and their basal ends are 

 bridged by a wide plate on the pharyngeal floor. 



In Dissosteira there is at each side of the mouth, in the angle between 

 the dorsal arms of the suspensorial bar of the hypopharynx, a very 

 small but distinct membranous lobe of a definite form (fig. 42 B, Pnt), 

 but having no apparent function, and bearing neither hairs nor sense 



Ik 



