NO. 8 ANATOMICAL LIFE OF THE MOSQUITO — SNODGRASS S7 



The long, gutterlike labium of the mosquito is the so-called pre- 

 mentum of a generalized labium, the usual basal part of the labium 

 being absent, though a small postmental sclerite may be present in 

 other Nematocera (fig. 22 G, Pmt). The prementum in Diptera is 

 known as the theca because it ensheaths the other mouth parts. 

 Apically it bears two small movable lobes, the lobelia (fig. 20 F, Lbl), 

 and ends between them in a slender median projection, or ligula (Lig) . 

 The labella appear to be two-segmented, and evidently represent the 

 labial palpi because each is provided with an abductor and an adductor 

 muscle from the prementum. The only muscles attached on the base 

 of the labium are the two already noted that arise on the maxillary 

 stipites (J) and probably act as protractors of the maxilla, since the 

 labium is firmly fixed to the head. 



The sty li form mouth parts within the labial theca adhere to one 

 another in a compact fascicle. They are usually said to be held to- 

 gether by an oil liquid, but Bhatia and Wattal (1957) have described 

 rings issuing from the margins of the labrum that surround the 

 hypopharynx, mandibles, and maxillae and bind these stylets to the 

 labrum. However, no other investigator has reported the presence 

 of any such structures, and the writer has failed to see them in 

 Aedes, Culex, or Anopheles. The incurved lower edges of the labrum 

 enclose only the food canal. 



When the female mosquito is about to take a meal of blood, she 

 places the tip of the proboscis against the skin of the victim (fig. 

 21 A), closely holding the end of the stylet fascicle between the labial 

 labella. The movable maxillary stylets are the active piercing organs. 

 Acting alternately, first one is protracted and holds its position in 

 the flesh by means of its recurved teeth, then the other is forced in 

 beyond the first and takes a deeper hold. The labrum, mandibles, and 

 hypopharynx penetrate along with the maxillae. The retractor muscles 

 of the maxillae, instead of pulling the stylets out of the wound, where 

 they are held by the maxillary teeth, bring the head down closer to the 

 feeding surface. The labrum, still holding the stylet fascicle between 

 the labella, is thus forced to bend backward (B) and the bend becomes 

 greater the deeper the stylets penetrate (C). When finally the stylets 

 pierce and enter a small blood vessel, or let out a pool of blood, the 

 mandibles are drawn back from the end of the labrum to allow the 

 blood to enter the food canal in response to the suction of the cibarial 

 pump. Saliva discharged from the hypopharynx in some species serves 

 to prevent coagulation of the blood. A more detailed account of the 

 feeding act and of accompanying movements by the maxillary palpi is 



