Br VERA IBWIX-.SMITH. 431 



The effect is augiuonted by the actiim ol the peculiar mechanism at the 

 posterior end of the pharynx. This is a greatly thickened chitin structure, 

 wedge-shaped in ventral view, with bruad base at the posterior end (Plate xxxiii., 

 tigs. 3, 4). It takes the place of the dorsal pharyngeal wall, and projects, by 

 its downwardly curved under surface, into the space enclosed by the crescentic 

 ventral pharyngeal wall. It is attached to the ventral wall on each side by a 

 tough, dark-staining membrane, which appears to be similar in composition to 

 the dorsal wall higher up. Dorsally it projects upwards and outwards in the 

 form of two broad, stout, wing-like processes. Two powerful muscles, attached 

 to each wing, extend Ijaikwards to be inserted in the posterior margin of the 

 dorsai head plate (Plate xxxiii., figs. 1, 2). By the contraction of these 

 muscles the upper part of the "wing-bearer" would be pulled outward and 

 downward, while its ba.se would work against the face of the ventral wall (Plate 

 xxxiii., fig, 4). Apjiarently the reverse movement is effected by the elasticity 

 of the ligaments connecting it with the phaxynx anteriorly and laterally. I 

 cannot detect the presence of antagonistic muscles, although such muscles are 

 described by both Vaney and Jusbaschjanz. But, as the "Schlundkopf," or 

 masticatory apparatus, examined by tlieni was globular in form, it will be seen 

 that the details of its structure and relationships must necessarily be somewhat 

 different. 1 have not been able to find anything to correspond with the lateral 

 chitin plates which Jusbaschjanz describes as projecting up from the basal plate 

 of the wing-bearer, and connecting dorsally with the forked median plate which 

 bears the wings. However, as I have experienced great dilHculty in cutting this 

 apparatus and have not been able to get a complete series of sections, I cannot 

 speak with certainty of its structure throughout its entire length, or of the 

 exact way in which it connects with the dorsal pliaryngeal wall anteriorly. The 

 figures of transverse sections given here represent careful reconstructions of 

 those parts which I have been able to study in detail. 



In the region of the jiharynx immediately anterior to the "wing-bearer," 

 the dorsal wall has the appearance shown in Text-figures 22, 23. There is here 

 a short median process, to which the paii-s of dilator muscles are attached, and 

 which dift'ers but little in composition from the rest of the dorsal wall. 



Text-figures 24 to 26 represent transverse sections through different parts 

 of the wing-bearer itself. The first tapers from the broad base to a point dor- 

 sally : the next shows a broadening and slight forking of the dorsal portion, 

 the third the expansion into the two "wings." To the angles of tlie base are 

 attached the ligaments which connect it with the ventral wall, here seen torn 

 away from their connections in the sectioning. A broad layer of hypodermis 

 covers the dorsal surface of the wliole structure, and is continued along the 

 connecting ligaments. The "wing-bearer" consists of an outer layer of chitin, 

 staining dense brown, merging towards tlie interior into a clear pink, which 

 encloses a central core of much lighter and apparently softer composition. It 

 seems to be made up of a loose fibrous material, which is so transparent that, in 

 surface view, the wing-bearer has the appearance of being hollowed out in the 

 middle. But in transverse sections it is seen that this core broadens out into 

 a base which is deeply convex. 



In all the sections which I have examined, this liase and the ventral plate 

 present firtn, smooth surfaces to each other, but in the posterior part of the 

 apparatus there is a roughened appearance, suggesting denticles or other tooth- 

 like structures, on a much denser foundation, which I did not succeed in sec- 

 tioning. 



The wing-bearer measures 0.33 mm. in length, with a breadth of 0.30 mm. 

 to the tip of the wing. 



