G60 Laura Florence 



the free end of the lever and the wall of the trachea opposite the attach- 

 ment. No further description appeared until that of Mjoberg (1910:221), 

 who figures a single muscle attached to the free end of the lever, and 

 describes its insertion in the body wall near the stigma. At the close of a 

 detailed study of the stigmata of Heteroptera and Homoptera, Mammen 

 (1912:172) divides insect stigmata into four groups, according as they 

 have one extrinsic muscle, one intrinsic muscle, two muscles, or three 

 muscles, connected with the closing apparatus. Harrison (1916 a: 116) 

 gives a brief resume of the literature on the subject. He finds in Siphun- 

 culata (Anoplura) and in Mallophaga two muscles, which may be homol- 

 ogous with the " Musculus constrictor " and the " Musculus tenchnosus " 

 described by Solowiow (1909:707) in the caterpillar of Cossus cossus L. 

 Miiller (1915:30) refers to Landois' work on Phthirius, and says that he 

 himself could get no clear picture of the structure in Pediculus vestimenii 

 from the study of sections. 



Study of the hog louse has revealed a closing apparatus resembling that 

 of Heterodoxus longitarsus as figured by Harrison (1916a: 116), who 

 describes it as an intermediate type and gives no account of the muscula- 

 ture. The thoracic and abdominal stigmata are essentially the same 

 in structure and in mechanism, but the vestibule of the thoracic stigmata 

 is somewhat shorter, measuring approximately O.OS millimeter from the 

 surface of the stigma to the closing lever, while that of the abdominal 

 stigmata (Plate LIX, 3) measure? 0.11 millimeter. The approximate 

 diameter of the vestibule of the abdominal stigmata is 0.03 millimeter, 

 and at its inner end it narrows and both walls become strongly chitinized. 

 A chitinous lever about 0.03 millimeter long is attached to the ventral 

 wall, and the dorsal wall projects into the lumen as a sharp point. Beyond 

 the lever the wall continues strongly chitinized and somewhat convex 

 for a distance of about 0.016 millimeter, when it passes into the trachea 

 proper. This region corresponds to the bulla of Harrison. In gross dis- 

 sections no muscles have been found (Plate LIX, 2), but from the study 

 of sections cut at various angles there appear to be two muscles arising 

 from the free end of the lever. One of these is inserted in the convex 

 wall of the l)ulla, and the other in the botly wall just dorsad of the stigma. 

 This agrees with the fintlings of Harrison in other Siphunculata (Anoplura) 

 and in the Mallophaga. He offers two interpretations of the structure: 

 (1) both the extrinsic and the intrinsic muscle function in closing the 



