STRIDULATING ORGAN 115 



spiracles those most concerned in sound production, but that the anterior ones 

 also took part. He found that the insect was able to modulate the sounds within 

 a considerable compass and he explained this by the fact that the spiracles are 

 under the control of muscles. By means of these muscles tension can be exerted 

 upon the chitinous ring of the spiracle and the position of the membranes 

 changed and this, Landois thought, modulated the sounds. Landois further con- 

 sidered that the halteres helped to control the sound from the metathoracic 

 spiracles. 



Shipley and Wilson, in 1902, described a stridulating apparatus on the basal 

 part of the wings of Anopheles which is most probably the principal sound pro- 

 ducing organ. These authors call attention to the careful investigations of J. 

 Perez which prove, experimentally, that no sounds are produced by the stigmata. 

 Jousset de Bellesme reached the same conclusion and quite recently C. E. Pem- 

 berton has made experiments Math confirmatory results. This last investigator, 

 like Nuttall, found that if in removing the wing a stump remained the insect 

 continued to emit a sound ; if, however, the stump of the wing was entirely re- 

 moved, all perceptible sound ceased. 



The apparatus described by Shipley and Wilson is very complex and lies 

 among the series of nervures and ridges on the narrowed basal portion of the 

 wing. It consists of two structures which rest against each other and are capa- 

 ble of a certain limited amount of movement. " The anterior system consists of 

 a slightly movable bar, which covers a thickening in the tissue of the -wing. This 

 last-named ultimately passes into the subcostal nervure. The bar extends from 

 the articulation of the wing to the humeral cross-nervure, and, as we have stated, 

 we consider it to be slightly movable. On its hinder, free edge the bar carries a 

 series of thirteen to fifteen well-marked teeth, which, under certain circum- 

 stances, rasp across a series of ridges borne on the second part of the system." 

 This second part " consists primarily of a chitinous blade, shaped something 

 like a butcher's knife, which is ridged on its upper surface with thirteen to fifteen 

 sharply-defined elevations placed slightly obliquely. It is against these ridges 

 that the teeth of the bar mentioned above rasp. The relative position of the bar 

 and the blade is not constant. The latter is usually lying partly under the 

 former, but at times it is free from it, and it seems as though it were hinged at 

 the handle and can oscillate through a few degrees, around an axis at the base 

 of the proximal end. But it can not rotate very far. A little way behind the 

 back of the blade is an upstanding flange of the membranous tissue of the wing, 

 which we have called the trough. This trough catches and holds the blade, and 

 prevents the latter being thrown too far back." The authors then describe the 

 complex structures at the base of the wing which in their opinion constitute 

 part of the mechanism for producing sound by means of the above-described 

 organs. They further state that the area over which the blade travels is the only 

 part which "is quite smooth and entirely free from the minute hairs and 

 prominences which cover the rest of the wing." These authors also found cer- 

 tain minute structures upon the halteres which they thought might be used to 

 produce a sound, although they consider that the principal function of the 

 halteres is one of balancing and orientation. 



