373 



ORDER DIPTERA. 



Sub-order: Aphaniptera or Siphonaptera. 

 (Fleas.) (Plate 47.) 



Fleas are regarded by some authors as degenerated 

 dipterous insects, and are usually placed in a 

 special sub-order. 



Characteristics. — They are wingless insects which 

 have two pairs of tiny flaps — one pair on the meso- 

 thorax, and another pair on the metathorax, just in 

 the position where the wings are usually placed in 

 insects. These flaps are probably rudimentary 

 wings. 



Fleas are compressed vertically, and not laterally 

 (as is more usual with insects — for example, bug.^ 

 and cockroaches). This compression enables them 

 to get into crevices and cracks and hide in blankets, 

 and also to move easily in the fur of cats and hair 

 of dogs. The integument is segmented and 

 tough; it is of a bright, reddish brown colour and 

 is polished-looking. It is the breaking of this tough 

 skin which makes the ''crack!" in killing a flea. 



The head and thorax are not clearly marked off 

 from the body. The head is small. The eyes are 

 simple, not having the numerous facets of com- 

 pound eyes. Some fleas are said to be blind. 



The mouth (Plate 47, Fig. 1) is curious; it is 

 wonderfully fitted for its blood-sucking habits. 

 The mandibles or biting jaws are here, in the form 



