THe Hoa LousEt 661 
stiema, or (2) closing is effected by the intrinsic muscle and reopening 
by the extrinsic muscle. With Harrison, we consider the former the more 
reasonable explanation, in which case it is assumed that the trachea opens 
through its own elasticity on the relaxing of the closing muscles. 
THE MUSCULAR SYSTEM 
With the exception of Osborn’s (1904) note on the musculature of the 
protrusible disks and the claw, nothing has been published concerning 
the muscular system of the hog louse, and the only work on an allied 
species is that of Strébelt (1882, English trans. 1883:100) on Linognathus 
vituli (Haematopinus tenuirostris). Landois (1864:22, 1865 a:33, 39, and 
1865 b:495) described and figured a part of the musculature of the species 
affecting man, and was the first to observe the arrangement of the muscles 
in the female. Recently Miller (1915:10) has confirmed the work of 
Landois and has described in addition the arrangement of the muscles in 
the male. Nuttall (1917 a:295) has briefly mentioned and summarized 
the different arrangement of the abdominal muscle plates in the two 
sexes as described by Landois and Miiller. The musculature of the hog 
louse presents some striking contrasts to that of the pediculi infesting man. 
The head contains many muscles, of which the majority control the 
pharynx and the mouth parts and are described later in connecticn with 
those parts. The muscles controlling the antennae are confined to the 
head and the first segment of the antennae, those in the head all originating 
in the dorsal wall and none of them in the ventral as in the pediculi infesting 
man. There are six muscles, which originate in close succession on either 
side of the dorsal median line above the frontal ganglion and immediately 
posterior to the elevator muscles of the pumping pharynx. The two 
anterior muscles pass obliquely backward and downward, and are inserted 
in the ventral articulation of the antennae with the head; the two median 
muscles pass almost directly ventrad and are inserted in the dorsal 
articulation of the antennae with the head; and the two posterior muscles 
‘pass obliquely anterior and downward and are inserted immediately 
posterior to the median muscles. In the antennae the muscles are confined 
to the first segment, and consist of four bundles originating at the articu- 
ation of the antennae with the head and inserted two in the anterior and 
wo in the posterior articulation of segments 1 and 2. 
