Ture Hoa LousE : 659 
around, passing into the second pair of legs. The fifth branch leaves the 
plexus almost at the same point as the preceding, turns back, and enters 
the main trunk centrad of the point of issue of the tracheae of the third 
pair of legs, thus forming a loop, which may correspond to the thoracic 
tracheal triangle described by Harrison (1916 a:105) in some Mallophaga. 
There, however, the thoracic stigma forms the apex of the triangle, while 
this loop lies behind the stigma. Harrison suggests that the inner side 
of the triangle may be the only survival of wing tracheae. The sixth 
branch comes from the branch to the thoracic spiracle just dorsad of its 
entrance into the main trunk, and passes into the second pair of legs. 
As has been shown, two tracheae pass into each leg, one of which lies 
ventral and the other dorsal. In the coxae, branches are given off which 
break up into many fine tracheoles; in the femur a large branch is given 
off from each trachea, and one of these branches passes along with the 
main branches into the tibia, where the latter subdivide many times, 
passing into the spur, the pad, the tarsus, and the claw. 
The main trunks, on leaving the tracheal plexus, bend centrad and 
dorsad, passing into the head on either side of the esophagus and the aorta 
directly under the occipital apodeme. Just behind the sub-esophageal 
ganglion they diverge, and shortly give off a lateral branch to the neigh- 
boring muscles. Behind the brain a branch is given off centrad, and from 
its root the commissure of the sub-esophageal ganglion issues, while it 
passes forward close to the lateral borders of the brain. The main trunks 
continue forward alongside the antennal nerves, give off a branch to each 
antenna, and break up into numerous branches among the glands, the 
fat cells, and the sensory cells of the anterior region of the head. 
_ The external surface of the stigma resembles a cart wheel with an open 
hollow axis, and sections show the vestibule between the stigma and its 
trachea to be filled with hair-like, chitinous structures radiating from its 
‘inner surface to a thin wall surrounding a slender central canal (Plate LIX, 
8). These spoke-like projections doubtless prevent the entrance of foreign 
particles along with the air. A similar structure has been described by 
Miiller (1915:30) in the clothes louse. Between the vestibule and the 
trachea is inserted the closing apparatus, concerning the mechanism of 
which there is still some uncertainty. Krancher (1881:522-533) briefly 
described the structure in Haematopinus suis. His figure shows the 
nature of the vestibule, the closing lever, and one intrinsic muscle between 
