structure of the mouth-parts in the Body-louse 217 
carries a chitinous groove, the wall of which is much thickened, 
along its mid-dorsal line, and the thin flange-like margins, which 
are more or less folded up about the salivary duct and dorsal 
piercer, are crenate (Plate VII, Fig. 2). Its appearance in transverse 
section 1s shown in the various text-figures. At its anterior end it 
suddenly becomes much narrower, and terminates in a_bilobed, 
minutely denticulate, boring apparatus. Precise description of the 
component parts of the piercing apparatus is almost impossible, as, 
although the length of the apparatus as isolated from a potashed pre- 
paration is ‘622 mm., the width at the piercing apex is only ‘008 mm. 
| The tendons of the dorsal pair of muscles run along the sides 
of a short quadrilateral plate, from which runs forward the dorsal 
piercer, consisting of two thin curved plates, jommed by their con- 
tiguous edges, and which ends anteriorly in a bilobed denticulate 
tip, similar to the ventral piercer. A strand of tissue runs along 
the ventral side of the dorsal piercer for some distance, beneath 
which is suspended the chitinous salivary duct (Fig. 6). The latter, 
as far as I can determine, is the true salivary duct, but I have not 
been able to make out the connection with absolute certainty. 
This chitinous portion, in any case, takes its origin in the strand 
of tissue lying between the dorsal pair of retractor muscles, runs 
forward for some distance attached to the underside of the dorsal 
piercer, then lies free in the groove on the upper face of the ventral 
piercer. It ends a little short of the anterior extremities of the 
last-mentioned structures. 
The whole of this piercing apparatus enters the buccal tube 
through the ventral fissure, and is here bent at a definite angle. 
Into the piercer-sheath opens a pair of tubular glands, described 
by Pawlowsky (Plate VII, Fig. 1, p.gl.). These have a simple 
epithehal lining of small cells, very much smaller than any other 
gland cells in the body. Pawlowsky suggests that they may serve 
to lubricate the piercing organ, but I should think, from the small 
size of the cells and the absence of any sign of glandular activity 
in their protoplasm, that they are practically functionless. 
The musculature of the piercing apparatus comprises the three 
pairs of retractors already described, and a pair of large muscles 
which run from the postero-lateral region of the head on either 
side beneath the sheath, and are inserted into the tendons of a 
pair of small muscles rising ventro-laterally from the head-wall 
beneath the pumping-pharynx. These are the muscula digastrici 
of Pawlowsky, and probably serve, as he suggests, to draw the 
sheath with its contained apparatus forward, though it is a little 
difficult to understand just how this result 1s achieved. 
The action of this complex piercer 1s simply to make a wound. 
It is inserted by the action of the digastric muscles, aided possibly 
by differential action of the dorsal and lateral retractors; while by 
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