660 LavuRA FLORENCE 
the free end of the lever and the wall of the trachea opposite the attach- | 
ment. No further description appeared until that of Mjéberg (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 résumé 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 tendinosus ”’ 4 
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 vestimenti 
from the study of sections. 
describes it as an intermediate type and gives no account of the muscula-| 
ture. The thoracic and abdominal stigmata are essentially the same}. 
is somewhat shorter, measuring approximately 0.08 millimeter from .the 
surface of the stigma to the closing lever, while that of the abdominal} 
stigmata (Plate LIX, 3) measures 0.11 millimeter. The approximate} 
wall, and the dorsal wall projects into the lumen as a sharp point. Beyond 
the lever the wall continues strongly chitinized and somewhat convex), 
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 conve), 
wall of the bulla, and the other in the body wall just dorsad of the stigma}, 
This agrees with the findings 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 th}, 
