398 



DIPTERA. 



Fiar. 317. 



at its eud with the thu'd, and there is no intercalary vein. The 

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

 empodium. They hover in the hot sun 

 over and about flowers, resting upon 

 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 glohosus (Fig. 317 ; a, puparium ; 

 s, spiracular tubercles ; v, vent ; 6, 

 anterior view of the same ; c, larva just 

 before pupation) is found, according to 

 Mr. Sanborn, under sticks in company 

 with sliells. 



Milesia strikingly resembles, in its style of coloration and 

 form, the common large yellow wasp. The antennae are short, 

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

 bristle. M. excentrica Harris, with its yellow 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, witli two stigmata at the end, which the}^ pro- 

 trude out of the 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 eartli. The body of the larva shor- 

 tens and hardens, forming the puparium, which is provided 

 witli four horns, serving as organs of respiration. 



The species of Uristalis* are seen flying abundantly about 



* Jules Kunckel has recently detected a tiiie peritrachlal circulation in Eristalis, 

 thus confirming the discoveries of Blancliard and Agassiz. He saw the blood 

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

 trating into the capillary termination of those trachete, and saw the flow of the 

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

 to coiTcspond with the arterial circulation of the vertebrate animals, and the mi- 

 nute branches of the trache:e are capillaries, and the blood is arterial. "En 

 resume, the tracheaB of insects, air tubes in their central portion, blood vessels in 

 tlieir 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 oxygen ; it arrives at the capilla- 



