PROC. ENT. SOC. WASH., VOL. 23, NO. 1, JAN., 1921 5 



and B. Its distal end is loosely connected with the upper end 

 of plate A in the fully matured head. A chitinous plate lies 

 entad to the base of the second seta and its distal end (h] is 

 loosely connected with the occipital rim of the cranium. This 

 plate, however, has no connection with the seta and appears to 

 belong to the setal pouch. The remaining parts shown in this 

 figure may be identified by reference to the other drawings. 



There is here, indeed, an apparent analogy between the 

 musculature of the setae and that of the mandibles and maxillae 

 of biting insects, the retractors being the flexor muscles and the 

 protractors being the extensor muscles. The function of the 

 two sets is in a sense reversed, however, since in the Hemip- 

 tera the hard work falls on the protractors; and it must be admit- 

 ted that no other type of musculature could accomplish the out 

 and in motion of the setae. Hence, we must not give too much 

 weight to evidence based on the musculature purporting to 

 establish homologies between these two sets of organs. 



Figure 14 shows the apodemes of the first seta in the head of 

 an imago that has not yet escaped from the pupal skin. Head 

 plate B is cut off from C, and sclerite A^ carrying the hypy- 

 pharynx (Hphy], is swung forward. The membranous floor of 

 the groove between A and B is removed entirely and none of the 

 muscles (seen in figure 13) are shown. At this stage the muscle 

 plate (iPAp] shows a distinct central shaft having every 

 appearance of being of apodemal origin. Below, it disappears 

 in the wall of the funnel-shaped base of the seta. Above, it 

 fades away but the narrow upper end of the plate is fused with 

 head plate C at the point g a short distance below the origin 

 (ten] of the anterior arm of the tentorium. At a later stage both 

 of these connections appear to be with plate A, but this is due 

 to their fusing with the edge of the latter across the intervening 

 suture. In the fully matured head (fig. 13) the upper end (g) 

 of this plate (iPAp) is only loosely connected with sclerite A. 

 The retractor apodeme of the first seta (IRAp) at this early 

 stage arises independently from the hypoderm above the setal 

 base. When the head is mature the apodemal bases and the 

 seta are all consolidated into one continuous structure. 



Figure 15 is a median vertical section of the head illustrating 

 the mechanism of the pumping apparatus and showing also the 

 salivary glands and the salivary pump. The pharynx (Phy) is 

 a large bulb-like cavity with the front or dorsal wall (e) deeply 

 invaginated so that in the collapsed condition it almost fills the 

 interior. The sides of the pharynx are braced to the walls of 

 the head by complicated chitinous wings not shown in the figures. 

 The space between the mouth parts of insects is usually called 

 the mouth or buccal cavity, but it is properly only an external 

 space like that between the bases of the legs; the true mouth is 

 the lower part of the pharynx where the hypopharynx shuts 



