328 OUR HOUSEHOLD INSECTS 



spiracle, or breathing hole, the terminal orifice of a short 

 tracheal branch. Six spiracles are thus arranged along 

 each side, and the short branches from them join two 

 great tracheal trunks which run parallel to the margins 

 of the body. The whole body is covered with minute 

 scattered hairs, which are sharp-pointed and perfectly 

 straight. 



The legs are composed of the usual parts, but all the 

 joints are short and stout, giving an appearance of 

 clumsiness, and the feet are extremely peculiar, their 

 remarkable structure forming one of the distinctive 

 characteristics of a louse. The tarsus, or foot proper, 

 consists of two small joints, the division between which 

 is not very easy to see, and these are succeeded by a 

 terminal appendage in the form of a single, curved, 

 movable claw of large size, which is usually carried bent 

 more or less inwards, and is capable of being completely 

 folded back upon the foot. At the end of the tibia, or 

 shank, there is a movable pointed prominence, and by 

 means of this, which acts as a sort of thumb, and the 

 great claw, the insect is enabled to exercise that strong 

 grasping and clinging power for which it is noted, and 

 which is of great importance in its economy, facilitating 

 its movements amongst the hairs in the midst of which 

 its life is spent. In the figure one of the claws is shown 

 bent back upon the " thumb " as in the act of grasping. 

 The claws are very similar in shape to those of fleas, but 

 differ in being single on each foot, instead of double. 



In the structure of the mouth organs again, lice are 

 exceptional. When the dead or inactive insect is 

 examined, no mouth organs can be seen, for, when not 

 in actual use, they are retracted within the head. The 

 mouth is of the suctorial type, the insect feeding on 

 the blood of its victims, to obtain which, an incision 



