The Siphonaptera or Fleas 119 



THE SIPHONAPTERA OR FLEAS 



The Siphonaptera, or fleas (fig. 89) are wingless insects, with 

 highly chitinized and laterally compressed bodies. The mouth-parts 

 are formed for piercing and sucking. Compound eyes are lacking 

 but some species possess ocelli. The metamorphosis is complete. 



This group of parasites, concerning which little was known until 

 recently, has assumed a very great importance since it was learned 



89. Xenopsylla cheopis, male (x25). After Jordan and Rothschild. 



that fleas are the carriers of bubonic plague. Now over four hundred 

 species are known. Of these, several species commonly attack man. 

 The most common hominoxious species are Pulex irritans, Xenopsylla 

 cheopis, Ctenocephalus canis, Ctenocephalus fetis, Ceratophyllus 

 fasciatus and Dermatophilus penetrans, but many others will feed 

 readily on human blood if occasion arises. 



We shall treat in this place of the general biology and habits of 

 the hominoxious forms and reserve for the systematic section the 

 discussion of the characteristics of the different genera. 



