The Hog Louse 693 



areas in front of the head. When the spot for feeding has been selected, 

 the contraction of the dorsal and ventral protractor muscles, assisted 

 perhaps by the contraction of the tendon muscles in the side of the head, 

 moves forward the buccal plate and the pharynx, bringing the former 

 with the inclosed pumping pharyngeal tube in contact with the skin. 

 At the same time the haustellum is automatically pushed out, so everting 

 the buccal teeth, which anchor the head to the skin of the host; and the 

 sheath and piercers must also be carried forward, since the cuticula of 

 the sheath is continuous with that of the buccal cavity. Immediately 

 following the contraction of the protractors of the pharynx, the protractors 

 of the sheath and the piercers contract and telescope the hinder part 

 of the sheath into the front part, carrying with it the piercers and the 

 salivary duct, which are inserted into the skin of the host. Salivary 

 secretion passes into the wound, and probably contains an anti-coaguhn 

 similar to that demonstrated by Nuttall (1917 c: 74) in the saliva of 

 the man-infesting louse. The closing of the anterior sphincter of the 

 pharynx causes a negative pressure in the pumping pharynx, the dorsal 

 surface of which is meantime raised by the contraction of the dilator 

 muscles, and the blood flows through the canal of the dorsal piercers to 

 the pimiping pharyngeal tube and so to the pumping pharynx. When 

 the latter is filled with blood, the simultaneous relaxing of the interior 

 sphincter of the pharynx and of the dilator muscles of the pumping pharynx 

 drives the blood into the pharynx, whence it passes to the esophagus on 

 the relaxation of the posterior sphincter. From the esophagus the blood 

 is carried by peristalsis to the rest of the alimentary tract. The process 

 can best be seen in newly molted specimens, and is so rapid that the 

 muscles either act simultaneously or in very rapid succession. At the 

 close of feeding, the whole structure is brought to its resting position by 

 the' contraction of the retractor muscles and the relaxing of the pro- 

 tractors, while the elasticity of the plate imbedded in the floor of its 

 posterior region gives the final impetus to the piercers and the sheath. 



The wall of the mid-intestine consists of the usual four layers, a delicate 

 epithelium resting on a basement membrane and surrounded by inner 

 circular and outer longitudinal muscles which are arranged in a very 

 loose network comparable to that described by Cragg (1915:712) in the 

 bedbug. The epithelium of the stomach is similar throughout, no 

 definite areas being adapted respectively for secretion and absorption, 



