on the Structure of the Mouth in Pediculus. 229 
swine-louse, which certainly is much larger and stronger-built 
than the human species; and his result may be gathered from the 
following passage towards the conclusion of his treatise :— 
** According to these statements, the louse must go through four 
quite different acts when feeding through its haustellum. First, it 
must protrude the fleshy cone provided with hooks, and fix the 
hooks in the skin. This done, the second step is to push the horny 
semitube with the setee so far forward in the interior of the head as 
is necessary to let the more delicate sting appear outside the orifice 
of the fleshy cone. This act of protrusion is continued until the 
sting has reached the tissue containing blood, whereupon the inner 
tube, thirdly, acts as a drill and at the same time, moving-forwards 
and backwards, causes the ascent of the blood, if not by suction, 
certainly by capillary attraction. The fourth act is the peristaltic 
movement of the cesophagus, which keeps up the current of blood, 
and despatches further into the body the quantity of blood received 
into the cesophagus. This movement is that rhythmic pulsation 
which Swammerdam has compared to a pendulum.” —Linn. Entom. 
vol. ii. pp. 581, 582. 
As the solid part of the labium, even by pressure, very easily 
detaches itself from the soft producible part on which the barbs 
are fixed, itis not surprising that they should have separated 
during the dissection without Burmeister observing it. Thus 
it escaped his attention that they belong one to another, and 
the inner part of the labium became to him an independent 
horny semitube. But thereby he lost the right way out of the 
old error (caused in some measure by the misunderstanding of 
a certain passage in Swammerdam) of a soft proboscis capable of 
protrusion—a vagina mollis, as Nitzsch says, or a “ fleshy cone,” 
as Burmeister expresses himself. This circumstance, finally, 
prevented him from perceiving the conformity of this structure 
of mouth with that prevailmg amongst Rhynchota; nay, he 
does not even attempt to refer it to any known type of mouth, 
nor could such an attempt be successful as long as the imagi- 
nary “ fleshy cone” had not been disposed of. Burmeister’s 
statements concerning the structure of the inner tube agree 
tolerably well with my own; some smaller differences may with 
probability be explained as arising from the more considerable 
size and powerful structure of the swine-louse ; they would at any 
rate agree very well with the differences between the skin of man 
and that of swine. His hypothesis concerning the use of the 
tube during suction, which he conjectures to be partly to act as a 
drill and partly as the brake of a pump, if closely examined can- 
not be pronounced free from confusion and self-contradiction ; 
but it must in any case be remembered that that author, as 
indeed he expressly states in another part of his treatise, 
