structure of the mouth-parts in the Body-louse 213 
and dorso-lateral regions of the head wall, and which, upon con-— 
traction, raise the depressed roof, so that the chamber assumes an 
ellipsoid shape. In this condition the lateral cavities supported 
by the cornua are not nearly so conspicuous. In specimens which 
have been treated in potash, and then passed into glacial acetic 
acid, the chamber is invariably blown out into this ellipsoid shape. 
Posteriorly the lumen narrows, and ascends towards the pharynx. 
At the narrowest part a band of hair-like chitinous processes of 
the cuticle projects into lumen all round. These processes are 
referred to by Pawlowsky, who suggests that they may assist in 
closing the lumen, but I cannot see how they can serve such a 
purpose. They show no indication of any sensory function, and 
probably act as a mechanical straining apparatus to prevent any 
foreign particle from entering the pharynx. They are indicated 
in Plate VII, Fig. 1, ps. 
A valvular apparatus exists at the anterior end of the pumping- 
pharynx, which will be described in connection with the buccal 
tube. The function of this part of the stomatodaecum is very 
obvious. By the action of the dilatator muscles in raising the 
depressed roof, a negative pressure results, and blood is drawn 
into the cavity. By the closure of the anterior-valve, and the 
relaxation of the dilatators in order from before backwards, the 
blood is forced backwards into the pharynx. That the dilatators 
do relax in this way, and not all together, seems certain from a 
study of the feeding insect under a low power binocular, as the 
blood can be plainly seen to come and go in a manner reminiscent 
of the peristaltic process in the dorsal vessel of an annelid. 
Certain of the muscles inserted into the roof would seem to be 
at least partially concerned in the protraction of the pumping- 
pharynx, as they run forwards, as well as upwards, to be inserted 
into the ring of thickened chitin which almost completely surrounds 
the head at the level of the opening of the piercer-sheath into the 
buccal cavity. 
The pharynx and oesophagus. 
An ascending tube, slightly bent upon itself, and very short, 
connects the pumping-pharynx with the pharynx. I cannot follow 
Patton and Cragg’s account of this portion of the alimentary canal. 
They seem to me to have confused a short dorsal diverticulum at 
the anterior end of the pharynx, which for three or four successive 
sections appears as a separate cavity, and then cuts out, as a fold 
in the connecting tube. At its anterior end the pharynx shows 
a deep, fairly narrow, lumen in transverse section, which almost 
immediately becomes reduced to a smaller, X-shaped, lumen, 
owing to the presence of a powerful anterior sphincter (as. in 
Plate VII, Fig. 1). Behind the anterior sphincter three pairs of 
