DIPTERA, NEMOCERA. 349 



The flight of these insects is worth noticing, when we 

 consider the astonishing muscular power which must be 

 exerted by animals of weight so inconsiderable, in main- 

 taining their position against the wind. They generally 

 fly, or hover,* with their heads towards the wind, and a 

 cluster may be seen for hours dancing in the air without 

 yielding one inch of we cannot say ground ! The 

 loud humming, or trumpet-like sound too of the female, 

 if, as seems most probable, produced by the rapid 

 vibrations of the wings, must require a marvellous array 

 of powerful muscles. 



That this is indeed the case is easily to be seen in a 

 Gnat rendered transparent by soaking in turpentine and 

 then viewed by polarized light. The whole of the 

 bulky (!) thorax (the only part of a Gnat which seems 

 to have any solidity at all) appears crossed and re-crossed 

 at right angles by broad, band-like muscles, which (if 

 the selenite crystal be used in the examination), 

 actually gives the little creature the appearance of being 

 dressed in a large check tartan jacket ! A beautiful 

 economy of power is also to be noticed in the centraliza- 

 tion of the weight of the insect in this one part, by 

 which the poising of the body is effected without special 

 muscular effort. 



Eapidity of motion in these insects is in evident re- 

 spouse to quickness of vision. Though doubts are 

 entertained as to the distinctness of sight in insects 

 generally, there can be none concerning the swiftness 



* The verb to hover is used here and elsewhere to express the action of 

 flying, fluttering, or remaining as it were suspended over one spot, whether 

 this be as, when by the rapid action of the wings the insect is maintained 

 apparently motionless in the air (as in some Syrphidse, &c.), or as in the 

 limited dance of the Gnats. 



