THE COMMON FLEA 25! 



the head. To the thoracic segment are attached, as 

 usual, the three pairs of legs, which increase in length 

 from before backwards. 



The legs are remarkable in several ways. At first 

 sight they seem to have an extraordinary number of 

 joints, and yet the parts are exactly the same as in 

 insects generally, and follow the plan typified in the 

 cockroach. It will be remembered that that joint of an 

 insect's leg by which the limb is attached to the thorax 

 is called the coxa. Now the coxae of a flea are not only 

 enormously large, being indeed the broadest and almost 

 the longest section of the leg, but they are also far more 

 completely freed from the thorax than is usually the 

 case, being only attached by one extremity : this causes 

 the leg to appear to have an extra joint. But this is 

 not all. In the first pair, especially, we seem to have 

 yet another additional joint, and this appearance is due 

 to the fact that the epimera (viz., those elements of the 

 thoracic segment to which the coxae are directly attached) 

 themselves project from the body of the segment, and 

 point obliquely forwards. These arrangements give an 

 extremely awkward appearance to the legs, but no doubt 

 facilitate the leaping process. The trochanter is small, 

 and both femur and tibia are about the same length as 

 the coxa ; but the tarsus, which, like that of the cock- 

 roach, consists of five joints, is remarkably long, and is 

 terminated by a pair of long curved claws, which the 

 insect must find extremely useful as it works its way 

 about amongst the garments of its host, or between the 

 bed-clothes. Most leaping insects have the hind femora 

 very largely developed, since in them are placed the 

 muscles which originate the impulse of projection. This 

 arrangement is especially noticeable in grasshoppers, and 

 in the tiny beetles called turnip-fleas, which do so much 



