83 



Stylet, an unpaired slender piece lying below the maxillae. 

 This is the greatly developed hypopharynx.'^ These six 

 stylets, labrum, mandibles, maxillae, and hypopharynx are 

 the instruments with which the female horse-fly pierces the 

 skin of animals to get at the blood ; the male has no pierc- 

 ing stylets, and feeds on flower-pollen. 



Beneath the grouped stylets is the long trunk- or probos- 

 cis-like labium^ presenting on its upper surface a shallow fur- 

 row in which the stylets may be partially enclosed, and pre- 

 senting at its distal extremity a conspicuous, expanded, disk- 

 like part called the labella. This terminal disk is believed by 

 some entomologists to be composed of the greatly modified 

 labial palpi. It is made up of two fleshy lobes or leaves, 

 bearing on the outer or under surface many fine, transversal, 

 subparallel lines or ridges. The two lobes can be closed 

 together like the leaves of a book. 



Make a drawing showing all of the mouth-parts from the 

 dorsal view. The stylets can be spread apart laterad, so as 

 to expose the under ones. 



In only a few families of Diptera are free mandibles pres- 

 ent, and when present they are possessed, as already men- 

 tioned, only by the females. In many flies there are no 

 piercing stylets, and as representative of these flies without 

 piercing mouth-parts the common house-fly may be studied. 



MOUTH-PARTS OF THE HOUSE-FLY. 



(Musca domestica; order Diptera.) 



In the house-fly the mandibular and maxillar stylets being 

 gone, we find only the trunk-like labium, with the labrum- 

 epipharynx lying closely appressed to, and almost fused with 

 its dorsal surface, and the maxillary palpi. 



* The hypopharynx and the epipharynx (outgrowth from the upper wall of 

 the pharynx) are in most insects small, fleshy, and inconspicuous. 



