CH. ii] EXTERNAL STRUCTURE OF A FLEA 31 



it is the third joint from the body (femur) which is 

 so immensely enlarged. The three pairs of legs are 

 each attached to a different thoracic segment. 



When fleas walk, they are so to speak planti- 

 grades walking on the sole of the foot, and all the 

 tarsal or foot joints are applied to the surface of 

 the ground. The claws serve as grips so as to make 

 the most of any unevenness ; and thus the insect 

 drags itself along with surprising rapidity when it 

 moves through the hairy coat of a mammal. But 

 on an open surface fleas are not really rapid movers 

 compared with many other insects. 



The two claws on the end of each ultimate foot 

 segment are freely moveable and are in fact highly 

 modified bristles or setee. 



In all fleas one of the plates of the metathorax 

 (or hindmost thoracic segment) called the epimeron, 

 is large and prolonged towards the rear. It in- 

 variably bears a stigma. The epimeron is placed 

 laterally to the first abdominal tergite. The older 

 naturalists jumped to the conclusion that this was 

 the remains of a wing. The best judges have, how- 

 ever, formed a decided opinion that no trace of the 

 relic of a flying organ can be detected on the thorax 

 of a flea. Heymons, a German entomologist, has 

 also failed to detect any sign in dissections which he 

 has made of the larvae and the pupee. 



The epimeron is in fact neither a scale nor a 



