CHAP. VII 



DIPTERA OR TWO-WINGED FLIES 



439 



or the kind of beauty we admire, and as a few of the 

 creatures somewhat annoy us, the whole Order is only too 

 frequently included in the category of nuisances that we must 

 submit to. Moreover, the scavenger-habits that are revealed, 

 when we begin to study their lives, are very repugnant to many 

 persons. It is therefore no wonder that flies are not popular, 

 and that few are will- 



TTSl 



T 



ing to study them, or 

 to collect them for 

 observation. jSTever- 

 theless, Diptera have 

 considerable claims to 

 be classed as actually 

 the highest of Insects 

 physiologically, for it 

 is certainly in them 

 that the processes of a 

 complete life - history 

 are carried on with the 

 greatest rapidity and 

 that the phenomena 

 of metamorphosis have 



, f , FIG. 21 2. A Dipteron (Fam. Syrphidae), Cheilosia chryso- 



beeil most perfected. coma . Britain. A, Adult larva ; B, the pupa ; C, 

 A mao-o-ot hatchino 1 nymph, extracted from pupa; D, imago. (From 



WeyeubergL.) 



irom an egg, is able 



to grow with such rapidity that the work of its life in this 

 respect is completed in a few days ; then forming an impene- 

 trable skin it dissolves itself almost completely ; solidifying sub- 

 sequently to a sort of jelly, it in a few days reconstructs itself 

 as a being of totally different appearance and habits, in all 

 its structures so profoundly changed from what it was that the 

 resources of science are severely taxed to demonstrate any 

 identity of the organs of the two instars. 



A good study of the comparative anatomy of Diptera has never 

 been made ; Baron Osten Sacken, one of our most accomplished 

 Dipterologists, has recently stated that " the external characters 

 of the Diptera have as yet been very insufficiently studied." 

 We shall therefore only trouble the student with a few observa- 

 tions on points of structure that are of special importance, or 

 that he will find frequently alluded to. The head is remarkable 



