structure of the mouth-parts in the Body-louse 215 
ganglion. It then bends upwards and enters the thorax between 
the main tracheal trunks, and opens into the ventriculus towards 
the hinder margin of the thorax. Pawlowsky states (1906, 
p- 202) that the wall of the oesophagus contains no muscular 
elements, but this 1s not the case. In sections they are not 
discernible, but in dissections the appearance of the wall leaves 
no doubt that both longitudinal and transverse fibres are present. 
I have not been able to make out any duct entering any part 
of the stomatodaeum so far described. 
The buccal tube. 
I first observed this structure in glycerine cleared larvae, in 
which it appeared as a delicate hyaline tube projecting into the 
buccal cavity, and seemingly in direct continuity with the pumping- 
pharynx, separated only by what looked like a valvular apparatus 
folded back into the cavity of the latter. The wall appeared to consist 
of delicate white chitin, transversely striated. At this time I had 
no sections, and as the structure had not been described in any 
previous account, I was quite at a loss to account for it, especially 
as it was not comparable with any structure with which I was 
familar in the comparative anatomy of the insect mouth. 
In section it is shown to be formed of two apposable half-tubes 
(Figs. 2, 3, b.twb.), and not of a single tube. These half-tubes take 
origin from the floor of the buccal cavity at its junction with the 
pumping-pharynx, and immediately behind the opening of the 
piercer-sheath. Pads of tissue of a peculiar kind underlie their 
bases, which appear to contain muscular elements, but the precise 
histological nature of which I have not been able to determine. 
After lying in the wall of the buccal cavity for a short distance, the 
half-tubes become free, and run forward as chitinous structures, 
forming a tube with approximately half the diameter of the 
surrounding cavity. The piercing apparatus enters into this tube 
through the ventral fissure, and runs forward within it. The tube 
ends abruptly beneath the end of the buccal plate, the piercer in 
the retracted condition projecting a little beyond its anterior end. 
How Pawlowsky missed this structure I cannot imagine, since he 
has figured a section (1906, p. 201, Fig. 8) passing through the 
base of it, which he letters as the mundhohle, though the large 
buccal cavity is shown lying dorsal to it. 
The exact relations of what I have referred to above as a val- 
vular apparatus cannot be satisfactorily determined from sections. 
What I suggest is partly an interpretation of the appearance seen 
in cleared preparations, partly an assumption. If the buccal tube 
is to be functional for the only purpose which it can possibly serve, 
that of a sucking tube, any means of communication between the 
