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 
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 cams, Ctenocephalus jelis, 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. 
