Production of Sound in a S.A. Locustid 67 



apparatus such as is found in the male. In the immature male, 

 about half-grown, the tonotegmina resemble the vestigial tegmina 

 of the female in that they do not overlap, but are separated by 

 a space in the middle line; they are larger than those of the 

 female and are of a soft texture. 



Left tonotegmen of male: — This is strong, chitinous, and some- 

 what rectangular in shape. Towards the anterior margin along 

 >he ventral surface and situated transversely, there is a file-like 

 organ consisting of about 25 chitinous teeth next to each other and 

 raised in position; the position of the file is indicated on the 

 dorsal surface of the tonotegmen by a well-marked groove. The 

 tonotegmen shows no venation, but the file may be considered as 

 being a modified vein, which it undoubtedly is in the case of 

 other locustids, such as Microcentrum and Xiphidium. 



Near the point of attachment to the mesonotum and along the 

 posterior free margin, the edges of this tonotegmen are curved 

 under, and this forms a sort of resonant chamber, which increases 

 lihe intensity of the sound produced. 



Right tonotegmen of male : — This is also chitinous and is some- 

 what more rectangular than the left; the anterior half of the inner 

 edge is strongly chitinous and like a thin plate ; it scrapes the teeth 

 of the file on the left tonotegmen and thus the shrill sound is pro- 

 duced. On the ventral surface towards the anterior margin, and 

 situated transversely across the tonotegmen are about 16 chitinous 

 teeth. As in the left tonotegmen so here the free edges are 

 curved under along the posterior margin and near the point of 

 attachment. 



Production of the sound: — The stridulation can easily be 

 observed if a male be located and then approached carefully. If 

 the approach be sudden he will usually stop as soon as the obser- 

 ver is within a few feet, and will often attempt to escape by drop- 

 ping clumsily to the ground. In the natural position the left 

 tonotegmen overlaps the right. When stridulating it will be noted 

 that the male sits with his head and thorax somewhat depressed, 

 so that a large space is left between the posterior free portion 

 of the pronotum and the dorsal surface of the thorax. When 

 ready to begin, head and thorax, unless already in that position. 



