148 



AN INTRODUCTION TO ENTOMOLOGY 



and to the body-wall. Here each chordotonal organ is approxi- 

 mately T-shaped; the proximal nerve forming the body of theT; 



the scolopophore, one 



arm; and the chor- 

 dotonal ligament, the 



other arm. 



It will be observed 



that in this type of 



chordotonal organ 



the scolopophore and 



the ligament form a 



fiddle -string -like 



structure between two 



points in the wall of 



a single segment. It 



is believed that in cases 



of this kind the integu- Fig. 165. Diagram 



ment acts as a tympa- chordotonaV Organs 



Fig. i6 4 .-Chordotonal organ *um or sounding rfa^tTm^C^a- 

 of a larva of Chironomus board. u T ( 



(FromGraber). 



b. THE CHORDOTONAL ORGANS OF LARVAE 



Chordotonal organs have been observed in so many larvag that 

 we may infer that they are commonly present in larvae. These organs 

 are very simple compared with those of certain adult insects, described 

 later. Those figured in the preceding paragraphs will serve to illustrate 

 the typical form of larval chordotonal organs. Even in the more 

 complicated ones, there are comparatively few scolopophores ; and, as 

 a rule, they are not connected with specialized tympana, but extend 

 between distant parts of the body- wall, which probably acts as a sound- 

 ing board. 



In certain larvae, however, the scolopophores are attached to 

 specialized areas of the body-wall. Hess ('17) has shown that the 

 pleural discs of cerambycid larvae, which are situated one on each side 

 of several of the abdominal segments, serve as points of attachment 

 of scolopophores. 



C. THE CHORDOTONAL ORGANS OF THE ACRIDIID^E 



In the Acridiidae there are highly specialized ears situated one on 

 each side of the first abdominal segment. The external vibrating 



