CHAPTER VII 



THE FLEAS 



Order II. Siphonaptera. — Insecta (p. 15). Members of this order 

 have the body compressed laterally, and the color is usually dark brown. 

 The head is small, generally bearing a single ocellus on each side, com- 

 pound eyes are absent. The mouth parts are suctorial but differ from 

 those of the order Diptera in that the true haustellum is lacking, the 

 sucking structure consisting of the ventrally grooved labrum and the 

 two mandibles, which form a half -open tube (Fig. 36, e and f). The 

 maxillae are sharp and serve to puncture the skin. The three thoracic 

 segments are distinct, each bearing a pair of well-developed legs, the 

 posterior pair being especially long, powerful, and adapted for leaping, 

 which is the principal mode of progression. 



Metamorphosis is complete. The larvaj are long, slender, without 

 feet, and somewhat hairy. When mature the larva spins a cocoon and 

 enters upon a distinct pupal stage. During this stage the pupa takes 

 the form of the adult with the appendages enveloped in a hard pupal 

 case. At no stage in the metamorphosis are there traces of the supposed 

 ancestral wings. It is probable, however, that the fleas have descended 

 from winged forms, and they are usually considered as being closely 

 related to the Diptera. 



There are many species of fleas, most of them inhabiting various wild 

 birds and mammals. It will be sufficient here to consider the following 

 three of the family Pulicidse: 



1. Ctenocephalus cams, the dog flea. 



2. Ctenocephalus felis, the cat flea. 



3. Pulex irritans', the human flea. 



The two species of Ctenocephalus can easily be distinguished from 

 Pulex by the presence in the former of comb-like spines on the lower 

 margin of the head and on the hinder margin of the prothorax. These 

 spines are dark colored, stout and closely placed (Figs. 34 and 85). 

 The dog and cat flea have long been placed together under the one 

 species Pulex serraticeps, but a later classification recognizes a specific 

 difference based principally upon the form of the head. In Ctenoceph- 

 alus canis the head, when seen from the side, is rounded in front and 

 somewhat less than twice as long as high. The head of C. felis, seen from 

 the side, is more acute angled in front and is long, being fully twice as 

 long as high. The head of Pulex irritans, with its absence of spines, is 



