150 



AN INTRODUCTION TO ENTOMOLOGY 



many genera, these tympana 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- 

 _-S tailed accounts of these organs 

 have been published by Graber 

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

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

 ?pace, 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, 



Fig. 168. Section of Muller's organ; g, passing through the tympana and 

 ganglion-cells ; n, nerve; 5, s , scolo- the air-chambers formed by the 

 palae (After Graber). r , .. f ., , , / r .. 



folds of the body-wall. In the fol- 

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



Vri A >" ' arts P-v -HPS/ 



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

 num. 



a 



Fig. 170. Tibia of a locustid 

 with covered tympana; a, 

 front view: b, side view: o. 

 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 A branches, 



