STOUGH: THE HACKBERRY PSYLLA. 131 



attachment, holds that portion of the labium just beyond the 

 bend. Connected to the distal ends of these processes are mem- 

 branes which run cephalad between the bases of the pro- 

 thoracic coxae, surrounding the labium, to form a sort of fold 

 or groove for the same. This arrangement may be seen in 

 figure 2, plate XXIX, in diagram, m representing the mem- 

 brane surrounding the labium, p the process holding labium to 

 thorax ; the position of the labium and setse may also be seen. 

 Figure 1, plate XXXI, a cross section through the base of the 

 mouth parts and procoxse, corresponds roughly to Meek's 

 "Fig. 13" for Cicada, and shows the great similarity between 

 the two forms. The bases of the membranes surrounding the 

 labium are here illustrated. 



The labium is slitted throughout its entire length. At its 

 base, where it is almost flat, it has only short, low, lateral 

 edges or flaps, and hence is broadly open, and the upper parts 

 of the mouth fit into this (29-2, 4). The labium, epipharynx 

 and setse all lie on the floor of the labium. Just at, or a little 

 beyond, the end of the epipharynx the lateral flaps become 

 larger and converge, their wavy margins fitting rather closely 

 together. From here on to the end of the labium these flaps do 

 not diverge again. Figure 6, plate XXXI, represents a cross 

 section of the first segment of the labium just beyond its bend. 

 Here the slit is seen to be held together by means of grooves 

 and ridges. There is also a depression on its caudal wall. The 

 lining of the labial canal is somewhat chitinized. On each side 

 of the canal are found two longitudinal muscles, m of the same 

 figure. The first labial segment is much roughened distally; 

 the second is quite short, chitinized, and bears sensory hairs 

 at its distal end ; the third segment is heavily chitinized, with 

 a pointed tip ending in two lateral, tonguelike processes. The 

 lateral outline of these is seen in figure 2, plate XXXI, and in 

 cephalic aspect in figure 3. The most notable feature of these 

 processes is the three large sense organs on each — large spines 

 on pegs. These same three sense organs are found on the 

 labium of Aleurodidse. This segment also bears several large 

 sensory hairs, two of which are much longer than the segment 

 itself. 



Pharynx. — This is tube-shaped, chitinized, spreading some- 

 what at its cephalic end (29-5, p) . Its ventral surface is 

 supplied with eight pairs of muscles and tendons, which run 



