The Hog Louse 661 



stigma, 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 sj^stem of the hog louse, and the only work on an allied 

 species is that of Strobelt (1882, English trans. 1883:100) on Linognathus 

 vituli {Haeinatopinus 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 Miiller (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 hy Landois and Miiller. The musculature of the hog 

 louse presents some striking contrasts to that of the pediculi infesting man. 



The head contains manj^ muscles, of which the majority control the 

 pharynx and the mouth parts and arc described later in connection with 

 those parts. The muscles controlling the antennae arc 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- 

 lation of the antennae with the head and inserted two in the anterior and 

 two in the posterior articulation of segments 1 and 2. 



