Tue Hoa Louse 657 
passing among the viscera, pointing out the resemblance between them 
and the windpipe of man. Landois (1864:12, 1865 2:45, 1865 b:499) 
gave the first complete descriptions of the general respiratory system, 
describing in detail and figuring the closing apparatus of the tracheae of 
Phthirius. Then followed Strébelt’s (1882:106) description of Linognathus 
vitulr (Haematopinus tenuirostris). Both writers agreed in the general 
arrangement of the tracheae and the number of stigmata, but considered 
those of the abdomen as being situated on segments 2 to 7, an opinion 
held earlier by Denny (1842:34) and later by Stevenson (1995:15) and by 
Neumann (1911:407). Myéberg (1910:218) described the general system 
for Siphunculata (Anoplura) and compared it with that of Mallophaga. 
Harrison (1916a:101) worked on the respiratory system of the Mallo- 
phaga, and used Siphunculata (Anoplura) for comparative purposes. His 
results confirmed the earlier work of Mjéberg, who had pointed out the 
marked resemblance between the Siphunculata (Anoplura) and the less 
specialized formsof the Mallophaga. In thesame year Miller (1915: 29-32) 
described and figured the respiratory system in the clothes louse. 
In the hog louse there are fourteen stigmata, the typical number foi 
Siphunculata (Anoplura) — one pair on the thorax in line with the second 
pair of legs, and six pairs on segments 3 to 8 of the abdomen. The 
abdominal stigmata on segments 3 to 6 lie on the dorsal transverse 
median line, while those on segments 7 and 8 are more posterior and 
lateral in position and can be seen from both dorsal and ventral aspects. 
The stigmata are slightly raised above the integument and are sur- 
rounded by a stout chitinous band, the peritreme. The thoracic stigmata 
are oblong-ovate, measuring from 0.06 to 0.07 millimeter at the widest 
part, and the abdominal stigmata are circular, with a diameter of about 0.05 
millimeter. 
The respiratory system (Plate LIX, 1) consists of two lateral tracheal 
trunks extending the whole length of the insect, a posterior abdominal 
commissure, and four more slender commissures in connection with the 
main ganglia. In the abdomen the main tracheae lie near the dorsal 
surface on either side of the alimentary tract, and are united posteriorly 
in segment 8 by a commissure of diameter equal to their own, from which 
numerous fine branches pass to the fat cells of segment 9. In segments 
8 to 3 a branch is given off from each main trunk to the stigmata of the 
segment, and they in turn each send off two slenderer branches which, 
