464 OTHER BLOOD-SUCKIXC, FLIES 



distiiiKuisliod readily from other insects 1)\- the fact that there 

 is only one pair of membranous wings, the second pair of wings 

 being represented only by an insignificant pair of knobbed 

 rodlike appendages known as haltcrcs (Fig. 191, halt.)- The 

 head is joined to the thorax by a very slender flexible neck. The 

 thorax itself consists of one mass on account of the fusion of its 

 three component parts, and the abdomen consists of from four 

 to nine visible segments and is terminated by the ovipositors 

 or egg-laying organs in the female, and by the copulatory organs 

 in the male. The head is provided with a pair of antennae, a 

 pair of maxillary palpi and a proboscis composed of or con- 

 taining the mouthparts. The antennae and also the palpi are of 

 considerable use in classification; the extent of the variations in 

 the antennaj may be. gathered from Fig. 211. The mouthparts 

 are profoundly modified in accordance with the habits of the 

 flies. In the botflies, in which the adults live only long enough 

 to reproduce their kind, the mouthparts and even the mouth are 

 much degenerated; in the non-blood-sucking forms, such as the 

 common housefly, the mouthparts are more or less fused into a 

 fleshy proboscis which is used for lapping up dissolved foods; 

 in the blood-suckers, which are the forms that particularly in- 

 terest us here, the mouthparts are developed into an efficient 

 sucking and piercing apparatus. In some, e.g., mosquitoes 

 (Fig. 190) and horseflies (Fig. 225), the lower lip acts as a sheath 

 for the other parts which are fitted for piercing and sucking; 

 in others, e.g., the stable-fly, Stomoxys (Fig. 240), and the tsetse 

 flies, Glossina (Fig. 229), the lower lip itself forms a piercing organ, 

 and the epipharynx and hypopharynx form a sucking tube, the 

 mandibles and maxilla:^ ])eing absent. 



Life Histories. — All of the Diptera have a complete metamor- 

 phosis (see p. 329), and sometimes undergo a most profound 

 remodeling of the entire body during the usually short i)upal 

 stage. The life history, beyond the fact that a complete meta- 

 morphosis occurs, varies within very wide limits. Most flies lay 

 eggs, but some, e.g., the screw-worm fly, CochUomijia (or Chryso- 

 myin), and allied species, produce newly hatched larvie or eggs 

 which are just at the point of hatching, wiiile still others, e.g., 

 the tsetse flies, Glossina. do not deposit their ofTspring until it 

 has undergone its whol({ larval development and is ready to 

 pupate. 



