CHAPTER XVII. 

 SIPHONAPTERA. 



This order includes but one class of insects, the fleas. 

 By early entomologists, the fleas were classed as a family 

 of the Dipt era, on the ground that they were structurally 

 flies that had lost their wings through a process of degen- 

 eration, growing out of an increasing habit of parasitism. 

 But their structural differences are now known to be so 

 great that they are made to occupy an order by them- 

 selves. 



They are parasitic upon mammals and birds; hardly 

 any warm-blooded animals are exempt from their attacks. 

 The order, at present, consists of but a single family, the 

 Pulicidae. The insects are wingless, and have piercing, 

 sucking mouth parts. The body surface is heavily 

 chitinized and smooth, but is regularly set with spiny 

 hairs. The body is much flattened vertically, a fact that 

 makes it easy for the insect to pass readily between the 

 hairs of the dog, cat, or bear host, and also makes it 

 difficult to catch them. 



Among the most curious of the Siphonaptera are the 

 jigger fleas, insects more common in warm countries than 

 in our own latitude. The male jigger flea is winged, and 

 leaps on or off the body of the host ; but the female lives 

 on the body of the host nearly her entire lifetime. When 

 the female is ready to lay her eggs, she burrows beneath 

 the skin of the host, which may be one of the lower animals 



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