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 the T; 



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 



integument acts as 



a tympanum or 



sounding board. 



Fig. 164. — Chordotonal organ 

 of a larva of Chironomus 

 (From Graber). 



Fig. 165. — Diagram 



representing the 



chordotonal organs 

 of a larva of Chiro- 

 nomus (After Gra- 

 ber). 



h. THE CHORDOTONAL ORGANS OF LARV^ 



Chordotonal organs have been observed in so many larvae that 

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

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

 later. Those figured in the preceding paragraphs will serve to illus- 

 trate 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 

 sounding board. 



In certain larvse, however, the scolopophores are attached to 

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

 pleural discs of cerambycid larvee, 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 LOCUSTID^ 



In the Locustidae there are highly specialized ears situated one on 

 each side of the first abdominal segment. The external vibrating 



