12 MEDICAL ENTOMOLOGY 



organs, rather than the bristle-like or stylet form of the first 

 subtype. That these mouthparts serve quite largely as cutting 

 structures is evident from the large wound made and the quan- 

 tity of blood drawn by the "bite" of a horsefly, especially one of 

 the larger species, such as the black horsefly (Tabanus atratus). 

 The labium is the conspicuous median portion, loosely ensheath- 

 ing the blades, and terminating in large lobelia. The mandibles 

 are distinctly flattened and sabre-like, while the maxilla are 

 narrower and provided with conspicuous palpi. The hypo- 

 pharynx and labrum-epipharynx are both lancet-like. In the 

 male these piercing parts are very weakly developed, and are not 

 useful as weapons of attack. 

 Draw and label parts. 



c. Third subtype the stablefiy. This subtype represents a 

 group of piercing flies in which the mouthparts are distinctly 

 specialized, and show, together with the next subtype, to what 

 extent these structures may become differentiated within the 

 same family of insects. 



The proboscis at rest is carried at the position of a bayonet 

 at charge, and is therefore provided with a prominent knee or 

 elbow, which portion is highly muscular. This conspicuous 

 organ is the labium, terminating in the labella, which are pro- 

 vided with a complex series of cutting and adhesive structures. 

 Within the folds of the labium and easily removable through 

 the upper groove lie two sharp, heavy, bristle-like structures, 

 the labrum, the uppermost and heavier stylet, and the hypo- 

 pharynx, a lower and weaker structure, the two forming, as 

 in other Muscidae, a sucking tube supported within the folds 

 of the labium. The maxillary palpi are less prominent than in 

 the other Muscidae, but are similarly located, at the proximal 

 end of the proboscis. 



Draw and label parts. 



d. Fourth subtype the housefly. Here the prominent fleshy 

 proboscis consists mainly of the labium, which terminates in a 

 pair of corrugated rasping organs, the labella, and is attached in 



