36 



ENTOMOLOGY FOR MEDICAL OFFICERS 



and serrated at the tip, the maxillse being much more 

 coarsely serrated than the mandibles; they are used with 

 the epipharynx for piercing the integument of the victim. 



In the blow-fly (Fig. 3) the labium is stout and fleshy, and 

 ends in a pair of large, oval, expansile labella ; its groove is 

 a deep trough, which is closed above by the epipharynx 

 and hypopharynx and so converted into a suctorial tube. 

 Mandibles and maxillae are not recognisable as independent 

 organs ; if they exist at all, which is very doubtful, they are 

 represented by short chitinous vestiges incorporated in the 

 labium. 



The maxillary palps vary in form, and are a useful means 



palp,.. 

 epiph. 



pseudolracfieae^^ /-/ff/6>/ 

 Pio. 3.— Head of Blow-fly. 



Pig. 4.— Thorax of Tsetse-fly. 



of classifying flies. In the flies that have long, slender, many- 

 segmented antennse the palps also, as a rule, are long, slender, 

 and flexible, and usually consist of 4 or 5 segments. In 

 the flies that have an antenna of 3 segments and a dorsal 

 bristle, such as the house-fly, the palps are unsegmented and 

 stiff In flies such as the gadfly the palps, which also are 

 stiff, are composed of 2 segments. In some flies (e.g. 

 Glossind) the palps form a loose adjustable sheath for the 

 proboscis. 



The thorax (Fig. 4) is deep, and has much the form of an 

 inverted pyramid. The three thoracic segments are firmly 

 united, though the sutures between them can be distinguished. 

 The prothorax is so much contracted that in a dorsal view 



