96 SUCKIING-LICE. 
tube, which is retracted if not in use; inside this tube is a 
fine bristle-like organ which can be introduced into the skin 
for the purpose of sucking blood. According to Schicedte it 
has the following construction: ‘‘the peculiar attenuation 
of the head in front of the antenne at once suggests to the 
practiced eye the existence of a mouth adapted for suction. 
The mouth differs from that of Rhynchota (as bed-bugs, 
etc.) generally, in the circumstance that the labium is capa- 
ble of being retracted into the upper part of the head, which 
therefore presents a little fold which is extended when the 
labium is protruded. In order to strengthen this part, a flat 
band of chitine is placed on the under surface, just as a shoe- 
maker puts a small piece of gutta-percha into the back of an 
india-rubber shoe; as, however, the chitine is not very elas- 
tic, this band is rather thinner in the middle, in order that it 
may bend and fold a little when the skin is not extended by 
the lower lip. The latter consists, as usual, of two hard 
lateral pieces, of which the fore ends are united by a mem- 
brane so that they form a tube, of which the interior cover- 
ing is a continuation of the elastic membrane in the top of 
the head; inside its orifice there are a number of small hooks, 
which assume different positions according to the degree of 
protrusion; if this is at its highest point the orifice is turned 
inside out, like a collar, whereby the small hooks are direct- 
ed backwards, so that they can serve as barbs. These are 
the movements which the animal executes after having first 
inserted the labium through a sweat-pore. When the hooks 
have got a firm hold, the first pair of sete (the real mandi- 
bles transformed) are protruded; these are, towards the 
points, united by a membrane so as to form a closed tube 
from which, again, is exserted the second pair of setz, or 
maxillz, which in the same manner are transformed into a 
tube ending in four small lobes placed crosswise. It follows 
that when the whole instrument is exserted, we perceive a 
long membraneous, flexible tube hanging down from the 
labium, and along the walls of this tube the setiform mandi- 
bles and maxille in the shape of long narrow bands of 
chitine. In this way the tube of suction can be made longer 
or shorter as required, and easily adjusted to the thickness 
