194 ENTOMOLOGY FOR MEDICAL OFFICERS 



In the PulicidcB, of which the common human flea {Pulex 

 irritans) may stand as a type, the thoracic segments are not 

 foreshortened, the coxse and femora of all the legs are much 

 dilated, the head is more or less conical, and the labial palps 

 consist of more than 3 segments. 



In the Sarcopsyllida, of which the jigger {Sarcopsylla or 

 Dermatophilus penetrans) may be taken as a type, the thoracic 

 segments are much foreshortened, as if "telescoped," the 

 coxse and femora of the hind legs are only slightly dilated, 

 the head is angulated, and the labial palps, which are feebly 

 chitinised, consist of less than 3 segments, or even appear to 

 be unsegmented. 



For the determination of genera and identification of 

 species, specimens should be dehydrated in spirit, cleared in 

 oil of cloves, or xylol, or turpentine, and mounted in Canada 

 balsam. In the case of large specimens it will be necessary 

 first of all to soften them in caustic potash solution, and 

 perhaps also to bleach them slightly in peroxide of hydrogen. 



Family PULICID^. 



The following is a synopsis of the necessary genera : — 



Eyes well developed (comb on head and pronotum absent or 

 present) = 2. 



Eyes absent or vestigial (comb, or teeth, on head and pronotum 

 always present) = g. 



'No comb on head or pronotum = 3. 



A comb on pronotum only = 4. 



A comb on pronotum and two teeth on cheek, at the genal angle 



= Chiastopsylla, 

 A comb on pronotum and on lower edge of head 



= Ctenocephaltu. 

 'Sternum of mesothorax divided by an internal chitinous thickening 

 which runs obliquely forward from the coxal articulation 



= PuIbx 

 Sternum of mesothorax divided by two internal chitinous thicken- 

 ings,' one as in Pulex, the other running vertically upwards 

 from the coxal articulation to the upper border of the meso- 



sternum v j. ji 



= Xenopsylla. 



rPygidium not freely projecting _ 



4. \ Pygidium strongly convex and freely projecting behind ~ 



= Pygiopsylla. 



2- \ 



