The Hog Louse 657 



passing among the viscera, pointing out the resemblance between them 

 and the windpipe of man. Landois (1864:12, 18G5a:45, 1865b:499) 

 gave the first complete descriptions of the general respiratory sj^stem, 

 describing in detail and figuring the closing apparatus of the tracheae of 

 Phthirius. Then followed Strobelt's (1882: 106) description oi Linognaihus 

 vituli (Flaematopinus tenuirostris) . Both writers agreed in the general 

 arrangement of the tracheae and the number of stigmata, but considered 

 those of the abdomen as Ijeing situated on segments 2 to 7, an opinion 

 held earlier by Denny (1842:34) and later by Stevenson (1905: 15) and by 

 Neumann (1911:407). Mjoberg (1910:218) described the general S3rstem 

 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 Mjoberg, who had pointed out the 

 marked resemblance between the Siphunculata (Anoplura) and the less 

 specialized forms of the Mallophaga. In the same year Mtiller (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 postei'ior 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 

 mUluneter. 



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 thej'' in turn each send off two slenderer branches which. 



