362 DIPTERA. 



thereby, states that the fly, which produces the sound of F. vi- 

 brates its wings 352 times a second, and the bee, which makes 

 the sound of A', 440 times a second. "On the contrar}^ a tired 

 bee hums on E', and therefore vibrates its wings only 330 times 

 in a second. This difference is probably involuntarj^, but the 

 change of 'tone' is evidently under the command of the Avill. 

 and thus offers another point of similarit}^ to a true ' voice.' 

 A bee in the pursuit of honey hums continually and content- 

 edl}'' on A', but if it is excited or angry it produces a ver}' dif- 

 ferent note. Thus, then, the sounds of insects do not merely 

 serve to bring the sexes together ; they are not merely ' love 

 songs,' but also serve, like any true language, to express the 

 feelings. (Sir John Lubbock's Address before the London 

 Entomological Society, 18G8.) 



Landois describes the sound-producing organs in several 

 genera of flies. "He distinguishes three different tones as 

 emitted by these insects : during flight, a relativel}' low tone, 

 a higher one when the wings are held so as to prevent their 

 vibrating, and a higher still when the fly is held so that all mo- 

 tion of the external parts is prevented. The last mentioned 

 is the true voice of the insect ; it is produced In* the stigmata 

 of the thorax, and may be heard when every other part of the 

 body is cut awaj^ The first sound is caused by the rapid vi- 

 bration of the Avings in the air ; the second is caused, or at all 

 events accompanied, by the vibration and friction of the abdo- 

 minal segments, and bj^ a violent movement of the head 

 against the anterior wall of the thorax." The halteres also 

 assist in producing the sound. The vibration of the head in 

 the Diptera during the emission of sound is regarded bj' this 

 author as due to the transmission of movement from the tho- 

 rax. (Zoological Record, 1867.) Landois also states that 

 there are small species which give a deeper note than larger 

 ones, on account of the wing-vibrations not being of the same 

 number in a given time. (Lubbock.) 



The legs are slender, unarmed, except with stout bristles, as 

 in Asilus ; the joints are simple, cylindrical ; the tarsi are five- 

 jointed, the terminal joint ending in two claws (ungues), be- 

 tween which is the cusliion, or jmJviUus, consisting of two or 

 three fleshj^ vesicles, often armed with hairs, which are tubular, 



