96 SUCKIING-LICE. 



tube, which is retracted if not in use; inside this tuloe is a 

 fine bristle-like organ which can be introduced into the skin 

 for the purpose of sucking blood. According to Schioedte it 

 has the following construction: "the peculiar attenuation 

 of the head in front of the antennae 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 setee (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 setae, or 

 maxillae, \vhich 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 maxillae 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 



