152 



AN INTRODUCTION TO ENTOMOLOGY 



171, Os) composed of nerve-endings, which are scolopophores of the 

 integumenta! type. Two nerves extend to this ganglion, one from 



each side of the leg, and 

 each divides into many 

 scolopophores. The 

 attachment fibers of the 

 scolopophores converge 

 and are attached to the 

 wall of the leg. Two 

 terms have been applied 

 to this organ, both indicat- 

 ing its position in the leg; 

 one refers to the fact that 

 it is above the tympana, 

 the other, that it is below 

 the knee. 



The intermediate or- 

 gan. Immediately below 

 Fig. 172 .-Transverse section of the fore tibia of th supra _tvmpanal organ, 

 Decticus verrucivorus (From Berlese after - A 



Schwabe). In comparing this figure with the and between it and the 

 preceding, note that in that one the external described in the next 



parts are at the left, in this one, at the right. 



paragraph, is a ganglion 



composed of scolopophores of the subintegumental type ; this is 

 termed the intermediate organ (Fig. 171, Oi) . 



Siebold's organ or the crista acustica. On the outer face of the 

 front branch of the large trachea of the leg there is a third chordo- 

 tonal organ, the Siebold's organ or the crista acusitca. A surface view 

 of the organ is given in Figure 171 and a cross-section is represented in 

 Figure 172. It consists of a series of scolopophores of the subintegu- 

 mental type, which diminish in length toward the distal end of the 

 organ (Fig. 171). The relation of Siebold's organ to the trachea is 

 shown in Figure 172. It forms a ridge or crest on the trachea, shown 

 in setion at cr in Figure 172 ; this suggested the name crista acustica, 

 usedcby some writers. 



6. THE JOHNSTON S ORGAN 



There has been found in the pedicel of the antenna of many insects, 

 representing several of the orders, an organ of hearing, which is known 

 as the Johnston s organ y having been pointed out by Christopher 

 Johnston (1855). This organ varies somewhat in form in different 



