PARASITES. 225 



internals, leaving the vital parts untouched, until there is no longer 

 any necessity to prolong the life of the victim. 



I now propose to say a few words on the mouth parts of the 

 parasites which are free during their whole life : — the mosquitoes or 

 gnats, fleas, human lice, and the Mallophaga^ or biting lice. In 

 these creatures, except the Mallophaga, a puncture is made by a 

 combination of perforating lancets (if they may be so called), 

 which constitute the mouth-organs, and which, when combined, 

 form a sucking-tube, through which they draw up the juices of 

 their prey for their nourishment. This act is usually followed by 

 pain, swelling, and inflammation; but it is not known whether 

 these discomforts are caused by actual poison or by an irritating 

 action of the saliva ; at all events, no poison-glands are discover- 

 able. Of course., these wounds may occasionally be inflicted for 

 protective purposes, as well as for a means of procuring food. 



In the mosquitoes, or gnats, the blood-sucking propensity 

 belongs only to what we usually term the gentler sex, the males 

 being innocent and inoffensive (as far as animals are concerned), 

 and all the virulence being found only in the female mouth. To 

 this rule the fleas and bugs form an exception (and also the lice ?). 

 In them both sexes possess and use the piercing apparatus. 



The mouth-parts in the gnat are seven in number. The most 

 conspicuous is the labium - a long, flexible organ proceeding from 

 the front of the head and deeply grooved on its upper surface for 

 the reception of the others, and covered with hairs and scales. 

 The anterior extremity is divided into two lobes. The six remain- 

 ing parts consist of the labrum, which is stouter than the remaining 

 organs and grooved. It serves to direct and protect the other five, 

 which consist of a pair of mandibles furnished at the tips with 

 saw-teeth and a sharp point, a pair of similar but more slender 

 organs having thin blades, and a back without teeth, representing 

 the maxillae, to the base of which the palpi are attached ; and a 

 very fine instrument, ribbed up the middle, and traversed by a 

 tube, terminated by a somewhat spear-shaped head — this repre- 

 sents the tongue. 



When the female attacks her prey, she places the lobes of the 

 labium upon the spot selected, and the piercing-organs enter the 

 skin, being guided and supported by the labium. As they pene- 



