370 MR A. E. SHIPLEY AND MR EDWIN WILSON ON A 



' The obvious explanation of the higher note given off by the males is that their 

 ' wings are markedly narrower and shorter than those of the females. Although a 

 ' female Culex pipiens gave a higher-pitched note than a female A. maculipennis, we 

 ' are not at all sure that it was not simply due to the smaller size of the former insect. 

 ' The male of this species of Culex certainly gave a higher-pitched note than the 

 ' female.' * 



In' the experiments described above, the note increased in pitch as the wings were 

 shortened, until a very short stump was left. As long as these stumps were left on the 

 body, a note was heard. These stumps would certainly include the stridulating 

 apparatus figured on Plate, which lies very close to the thorax at the base of the 

 wings. Dr Nuttall assures us that when these stumps were removed, all perceptible 

 sound ceased. Thus it appears, that as long as the very small portion of the wing 

 which includes the stridulating organ remains on the body, a note is heard, but when 

 this be removed no sound is perceived. This is evidence that the sound proceeds from 

 the base of the wings, and not from the spiracles or other parts of the thorax. 



Mons. J. Perez t has carefully gone into the question of the production of sound in 

 the Diptera. He shows, experimentally, that the stigmata take no part in the pro- 

 duction of sound. " Les causes du bourdonnement resident certainement dans les 

 ailes." He, too, points out that if the wings are cut short the note becomes more acute, 

 until the ' timbre ' resembles that of certain interruptors which break, and make an 

 electric conductor. This sound we should attribute to the stridulator described above. 

 Mons. Perez definitely states that both in the Diptera and in the Hymenoptera, the 

 buzzing is due to two causes, " l'une, les vibrations dont l'articulation de l'aile est le 

 siege et qui constituent le vrai bourdonnement ; l'autre, le frottement des ailes contre 

 l'air, effet qui modifie plus or moins le premier." The apparatus we have described is, 

 we believe, the mechanism by means of which his first vibrations are produced. 



In the same periodical \ Mons. Jousset de Bellesme confirms the statement that 

 both Dipterous and Hymenopterous insects emit two sounds, one deep and one acute, 

 and states that the latter is usually the octave of the former. It is this double note 

 which gives rise to the peculiar buzzing associated with these two orders of insects. 

 Mons. de Bellesme, like Mons. Perez, discards the view that acute sounds are due to 

 any action of the issuing air in the stigmata, and attributes it to the vibrations of the 

 pieces of the thorax which support the wing, and which are moved by the muscles of 

 flight. It is usually stated that these muscles are not inserted into the wing, but into 

 the sides of the thorax, to which the wing is so attached, that when the lateral walls of 

 this part of the body are deformed by the action of the muscles, the wings move up and 

 down. But whether this be the case or not, it is clear that the vibrations of the sides 

 of the thorax caused by the muscles of flight — and causing the vibrations of the wing — 

 will synchronise in number with these wing vibrations, and will give forth the same 

 note. The existence of the higher note — ' usually the octave ' of the one produced by 



* /. Hygiene, ii., 1902, 77 /. t C. B. Ac. Paris, lxxxv'ii., 1878, p. 378. J Ibid., p. 535. 



