398 



DIPTERA. 



at its end with the third, and there is no intercalary vein. The 

 genital armor of the male is unsymmetrical, and there is no 

 empodinm. They hover in the hot snn 

 over and about flowers, resting npon 

 them to feed on their sweets. The 

 larvae either live in the water, when the 

 body ends in a long extensile breathing 

 tube ; or are terrestrial, living in decay 

 ing wood, or parasitically in nests of 

 bees, or, as in Syrphus, live among plant- 

 lice. The singular spherical larva of Mi- 

 crodon globosus (Fig. 317 ; a, puparium : 

 s, spiracular tubercles ; -y, vent ; b. 

 anterior view of the same ; c, lar^a just 

 before pupation) is found, according to 

 Mr. Sanborn, under sticks in company 

 with shells. 



Milesia strikingly resembles, in its style of coloration and 

 form, the common large j-ellow wasp. The antennae are short, 

 drooping, with a stout oval terminal joint, and a subterrainal 

 bristle. M. excentrica Harris, with its 3ellow spots and bands 

 resembles a wasp. 



EristaUs is well known by its aquatic "rat-tailed" larvae, the 

 abdomen terminating in a long respiratory tube equalling the 

 bod}^ in length, with two stigmata at the end, which they pro- 

 trude out of tlio water. There are seven pairs of prolegs, more 

 distinct than in any other genus in the entire suborder. The 

 pupa is found buried in the earth. The body of the larva shor- 

 tens and hardens, forming the puparium, which is provided 

 with four horns, serving as organs of respiration. 



The species of EristaUs^ are seen fl^'ing abundantly about 



*.Tules Kunrkcl has recently detecterl a true peritraeliial circulation in Eristalis, 

 thus conflrming the discoveries of Blanchard and Agassiz. He saw the blood 

 imprisoned between the inner air tube and the envelope of the trachea, and pene- 

 trating into tlie capillary termination of tliose trachefe, and saw the flow of the 

 blood globules in the peritracheal space. This peritracheal circulation thus seems 

 to coi-respond with the arterial cii-culation of the vertebrate animals, and the mi- 

 nute branches of the trachete are capillaries, and the blood is arterial. "En 

 resume, the tracheaj of insects, air tubes in tiieir central portion, blood vessels in 

 their peripheral portion [i. e., the space surrounding the air tube] become at their 

 extremities true arterial capillaries." "The blood in the peritracheal space re- 

 mains through all its course in contact with the oxj^geu; it arrives at the capilla- 



