40 THE FLEA [CH. 



to deal with each of these in turn and then to explain 

 how they act in combination. 



The maxillce. These are a pair of horny or 

 chitinous triangular plates one on either side of the 

 flea's face. They are placed some distance away from 

 the orifice of the mouth and to the right and left of 

 it. They do not serve for piercing or sucking, and 

 appear to have no active function unless they serve 

 to separate the hairs of the host and enable the flea 

 to reach the bare skin. In the majority of bat -fleas 

 (Ceratopsyllidce) the maxillae are dumb-bell-shaped 

 but in all other fleas they are more or less triangular. 

 From the fore part of each springs a palpus. Like 

 other highly chitinised parts of a flea, the maxillae 

 are usually dark in colour. 



The maxillary palpi. These are jointed hairy 

 feelers which project forwards and were mistaken by 

 the older naturalists for antennae. They spring from 

 the base of each of the maxillee where these latter 

 organs are joined to the head of the flea. The palpi 

 are sense-organs as the number of sensitive hairs on 

 their surface indicates. The maxillary palpi of fleas 

 are always composed of four segments. 



The labium and labial palpi. These form to- 

 gether what is called the rostrum of a flea. The 

 labium is a single organ which projects beneath the 

 aperture of the mouth. It may be described as the 

 lower lip of the flea. At its end it divides into two 



