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structure of the mouth-purts in the Body-louse 209 
‘than anteriorly. Upon the floor of this cavity, near its hinder end, 
‘opens a long invagination, the piercer-sheath, which extends 
beneath the alimentary canal back almost to the occiput, and 
contains the piercing apparatus. The pumping-pharyne is, in its 
dilated condition, ellipsoid, its long axis corresponding to that of 
the head, its posterior end higher than the anterior, its length 
‘12 mm. . In the resting condition it gives much the same section 
in both longitudinal and transverse sections, the floor and roof, 
with reference to the lumen, being concave and convex respec- 
tively. The pharyna, which has a length of ‘1 mm., is situated 
dorsally between the anterior cornua of the brain, and is X-shaped 
iN cross section owing to the action of powerful sphincters. It 
descends somewhat posteriorly, and passes into the oesophagus a 
narrow tube which passes downwards between the brain and sub- 
oesophageal ganglion, and runs backwards to join the mid-gut 
towards the posterior margin of the thorax. This gullet has an 
approximate length of ‘5 mm. 
Within the piercer-sheath lie four structures, which are 
directly continuous with six chitinous tendons, into which six 
muscles rising from the posterior wall of the head-capsule are 
inserted. The tendons of the dorsal muscles are continued into 
the dorsal-piercer, which throughout the greater- part of its 
length has the form in section of two brackets lying side by side 
thus ~~, with their contiguous edges fused. The tendons of the 
lateral pair of muscles concresce as the ventral-piercer, the precise 
structure of which will be discussed later. The tendons of the 
ventral muscles expand into a chitinous plate, separable into 
anterior and posterior portions, which lies embedded in the floor 
of the sheath. These plates may represent the mentum and sub- 
mentum of the labium. The fourth structure is a chitinous duct 
which is first attached by a strand of tissue to the ventral side of 
the dorsal-piercer, then becomes free, and lies in a groove on the 
dorsal surface of the ventral-piercer, and finally enters the buccal 
cavity equidistant between the two. This duct originates in 
paired strands of tissue arising from the ventral tendons, and 
passing into relation with the dorsal-piercer, and is, I believe, the 
salivary duct, although I have not been able to trace a definite 
connection with certainty, the structures being excessively 
minute. 
The structures so far indicated have been described with more 
or less success by previous workers. One important part of the 
apparatus has, however, hitherto altogether escaped notice. This 
part, which I call the buccal tube, is a tube lying free within the 
buccal cavity, composed of two lateral apposable half-tubes which 
arise ventro-laterally from the floor of the fore-gut at the point of 
junction of the buccal cavity and pumping-pharynx. Into the 
14—2 
