Tue Hoa LousEe 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-coagulin 
similar to that demonstrated by Nuttall (1917c: 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 pumping 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, 
