EARS 



317 



a stigma is placed close to the ear, and supplies the internal 

 structures of the organ with air. There are no stigmata on the 

 legs of Insects, consequently admission of air to the acoustic 

 apparatus in Locustidae is effected by means of a gaping orifice 

 at the back of the prothorax, just over the base of the front leg 

 (Fig. 101); this communicates with its fellow of the other side, 

 and from them there extend processes along the femora into the 

 tibiae, where they undergo dilatation, so as to form vesicular 

 cavities, one of which is in proximity to each drum of the ear. 

 These leg -tracheae are not con- 

 nected with the ordinary tracheal 

 system ; the prothoracic stigma 

 exists in close proximity to the 

 acoustic orifice we have described, -tr-n 

 but is much smaller than it. It 

 is not yet clear why the acoustic 

 apparatus should require a supply 

 of air apart from that which could 

 be afforded by the ordinary tracheal 

 system. This special arrangement 

 — ■ to which there is hardly a 

 parallel in Insect anatomy — has 

 still to be accounted for; we do 

 not know whether the necessity 

 for it may be connected with the 

 respiratory system or the acoustic 

 organ. 



The chief features of the acous- 

 tic apparatvis of the legs of Locus- 



tidae will be gathered from the 



accompanying diagrammatic trans- 

 verse section through the tibia. In 

 this figure the deep black parts 

 indicate the outer wall of the 

 tibia and its prolongations, the 

 white spaces indicate the parts 

 filled with air, while the dotted 

 portions are occupied by blood or some of the body organs 



^ The small space above Ini left free from dots is, we presume, due to an omission on the 

 part of Graber's artist, but we have not thought it right to interfere with his diagram. 



Fig. 194. -Diagram of arrangement of parts 

 of the ear as seen in transverse section of 

 the tibia of a Locustid. A, J, V, H, outer, 

 inner, anterior, posterior aspects of leg ; 

 fi,t^, thin part of integument forming an- 

 terior tympanum ; b, c, thicker portion 

 of same ; /, g, posterior tympanum ; 

 a, f, and d, h, g, thick portions of 

 integument ; i, k, internal protuber- 

 ances of same ; I, m, n, 0, walls of the 

 anterior tracheal vesicle, ^2^?";^:*, q, s, r, 

 walls of the posterior tracheal vesicle, 

 hTr ; 0", projection of tympanal orifice 

 of prothorax ; tr-n, tracheal nerve- 

 end organ, crista acustica ; st, rod ; 

 de, curtain - membrane ; hn, e, supra- 

 tympanal, nerve-end organ ; hn, gang- 

 lion cells ; st', rods ; 6, point of in- 

 tegumental fixation of nerve endings. 

 (After Graber.) 



1 the 



