Marshall—On the Anatomy of the Dragonfly. 
759 
difference between the two walls, external and internal, at 
their point of insertion. They probably help to elevate the 
upper lip. ; ; 
Buccal cavity. A view of the inner surface of the labruni 
show's, along and near its free outer margin, a number of long, 
slightly curved setae. Around the entire free margin there is 
a wide band, darker than the rest of the surface but which 
shows in section, no perceptible difference in the thickness of 
the cuticula. In the central region, wFere the sense pits are 
situated, the chitin is both darker and thicker ; where the 
epipharyngeal muscle is attached it is darker but not thicker^ 
There are also on the inner surface four groups of setae; two 5 
of theses are more centrally located, the other two groups are 
near the lateral margins (fig. 7). The setae comprising the 
more centrally located groups are longer than the others. In 
the central region there are a number of sensory plates; these 
are small, dark areas of the cuticula, of varying size and per¬ 
forated with small circular openings. The number of openings 
in each plate varies from one to thirteen; the greater number 
of openings in the larger plates give to them a sive-like appear¬ 
ance. 
Hear the center of the roof of the mouth, close to the upper, 
attached margin of the labrum, are two heavy, dark projec¬ 
tions of the chitin; these are covered with many stiff setae 
which gives to them a brush-like appearance (figs. 7, c and 8,c). 
From near the base of each brush there is a stiff, slightly 
curved chitinous rod which forms in part the inner margin 
of the labrum. These rods act as supports for the labrum and, 
near their outer ends, are found the hinges upon which it ar¬ 
ticulates. A little to the side from the apex of each brush 
there is a group of sensory pits. The layer of hypodermis 
which lies next to the cuticula shows but a slight variation in 
thickness; in the more central part the cells contain a great 
many black pigment granules. 
The hypopharynx is very large and leaves but little space 
underneath between it and the labium. Along its margin there 
are many setae, these are longer on the lower than on the 
