PARASITES OF ANIMALS. 37 



small piece of gutta-percha into the back of an India-rubber 

 shoe ; as, however, the chitine is not very elastic, 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 membrane so that they 

 form, a tube, of which the interior covering 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 directed backward, 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 setae (the real mandibles trans- 

 formed) are protruded ; these are, towards their points, united 

 by a membrane so as to form a closed tube, from which, 

 again, is exserted the second pair of setae, or maxillae, 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 membranous 

 flexible tube hanging down from the labium, and along the 

 walls of this tube the setiform mandibles 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 of the skin in the particular 

 place where the animal is sucking, whereby access to the 

 capillary system is secured at any part of the body. It is 

 apparent, from the whole structure of the instrument, that it 

 is by no means calculated for being used as a sting, but is 

 rather to be compared to a delicate elastic probe, in the use of 

 which the terminal lobes probably serve as feelers. As soon 

 as the capillary system is reached, the blood will at once 

 ascend into the narrow tube, after which the current is con- 

 tinued with increasing rapidity by means of the pulsation of 

 the pumping ventricle and the powerful peristaltic movement 

 of the digestive tube." 



