CHAPTER XXIX 

 ORDER SIPHONAPTERA* 



The Fleas 



The members of this order are small, wingless insects, in which the 

 body is laterally compressed, so that the transverse diameter is small, 

 the vertical one great. The mouth-parts are formed for piercing and suck- 

 ing. The metamorphosis is complete. 



The name of this order refers to the form of the mouth-parts and 

 to the wingless condition of these insects. 



These tiny tormentors are best known to us in the adult state; 

 for it is only "the adults that annoy us and our household pets. The 

 larv^as and pupae are rarely observed except by students who search 

 for them. 



The body of the adult is oval and greatly compressed, which allows 

 the insect to glide through the narrow spaces between the hairs of its 

 host. The integtmient is smooth, quite 

 hard, and armed with bristles, which 

 are arranged with great regularity (Fig. 

 1 1 2 1 ) and thus afford good characters for 

 distinguishing the different species. The 

 smoothness and firmness of the body 

 make it easy for the insect to escape when 

 caught between the fingers of man or the 

 teeth of lower animals. When once out 

 of the clutch of an enemy it quickly 

 leaps away. _ Fig. 1121.— The dog-flea and 



The head is broadly joined to the thor- 

 ax. There are no compomid eyes; but 



on each side of the head there is usually an unfaceted eye; these, 

 however, are sometimes wanting. Each antenna lies in a groove 

 somewhat behind and above the e^^e (Fig. 1122). The antennae are 

 three-jointed; the third joint, the flagellum, often called the club, 

 may be unsegmented, segmented on the posterior border only, or 

 completely segmented into several, usually nine, more or less separate 

 pseudo-segments (Fig. 11237!). There is usually an internal thicken- 

 ing of the body-wall extending over the vertex from one antennal 

 groove to the other (Fig. 1122, /), this is known as the falx or sickle- 

 shaped process. That part of the dorsal wall of the head in front 

 of the antennal groove and this thickening is termed, by writers on 

 the Siphonaptera, the/row5; the part behind them, the occiput; and 

 the lateral aspects of the head, below and behind the eyes, the gencB 

 or cheeks. 



A remarkable feature of the head of the Siphonaptera is the fact 

 that in the more generalized forms it is divided into two distinct 



*Siphonaptera : siphon (a-i<po}v) a tube; apteros {(Lwrepos) without wings. 

 C877) 



