398 



DIPTERA. 



Fig. 317. 



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

 genital armor of the male is nnsymmetrical, 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 3Ii- 

 croclon glohosus (Fig. 317 ; a, puparium ; 

 s, spiracular tubercles ; -y, vent ; 6, 

 anterior view of the same ; c, larva 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 yellow wasp. The antennae are short, 

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

 bristle. 31. excentrica Harris, with its j-ellow spots and bands 

 resembles a wasp. 



Eristalis is well known by its aquatic "rat-tailed" larvffi, 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 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 eai'th. The bod}' of the larva shor- 

 tens and hardens, forming the puparium, which is provided 

 with four horns, serving as organs of respiration. 



The species of Eristalis * are seen flying abundantly about 



* Jules Knnckel has recently detected <a true peritrachial circulation in Eristalis, 

 thus conflvming the discoveries of Blanchard and Agassiz. He saw the hlood 

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

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

 blood globules in the peritracheal space. Tliis peritracheal circulation tlnis seems 

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

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

 resume, the tracheaj of insects, air tubes in their centi-al portion, blood vessels in 

 their peripheral portion [t. c, 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 o.xj'gen; it arrives at the capilla- 



