150 



AN INTRODUCTION TO ENTOMOLOGY 



--S 



many genera, these t}Tnpana are exposed and easily observed (Fig. 

 169) ; but in some genera each is covered by a fold of the body-wall 



and is consequently within a cavity, 

 which communicates with the out- 

 side air by an elongated opening 

 (Fig. 170, a and b). 



Within the legs bearing these 

 tympana, there are complicated 

 chordotonal organs. Very de- 

 tailed accounts of these organs 

 have been pubhshed by Graber 

 ('76), Adelung ('92) and Schwabe 

 ('06); in this place, for lack of 

 space, only their more general 

 features can be described. 



Figure 171 represents a longi- 

 tudinal section of that part of a 

 fore tibia of Decticus verrucivorus in 

 which the chordotonal organs are 

 situated, and Figure 172 represents 

 a cross-section of the same tibia, 

 passing through the tympana and 

 s, s, scolo- ii^Q air-chambers formed by the 

 folds of the body-wall. In the fol- 

 lowing account the references, in most cases, are to both of these figures. 



Fig. 168. — Section of Mullet's organ 

 ganglion-cells; n, nerve; 

 palie (After Graber). 



Fig. 169. — Fore leg of a katydid; i, tympa- 

 ntun. 



a 



Fig. 1 70. — Tibia of a locustid 

 with covered tympana; a, 

 front view; &, side view; 0, 

 opening (After Schwabe). 



The trachea of the leg.— The trachea of the leg figured in part here 

 is remarkable for its great size and for its division into two branches, 



