THE TYMPANIC ORGANS OF THE BLOW-FLY. 629 



the similarity of the special nerve-terminals in both is indica- 

 tive of an auditory function. The innervation of the end 

 organs of the tympanic apparatus by the same nerve as the 

 halter is also worthy of note. If the sound is produced as I 

 have suggested, the tympanic apparatus may act as an audi- 

 tory mechanism especially sensitive to sounds having the same 

 pitch as those which the insect is capable of producing. On 

 the other hand, the range of vibrations capable of affecting the 

 halteres is probably larger. With our present knowledge, this 

 can only be regarded as a possible hypothesis, but it may serve 

 to indicate some line of observations in the future adapted to 

 throw more light on this intricate subject. 



14. CONCLUDING REMARKS ON THE PHENOMENA OF 

 HEARING IN INSECTS. 



The great variety in the form and size of the various chordo- 

 tonal organs, and the remarkable diversity of the structures with 

 which they are connected, suggests a few concluding remarks. 



As has been already stated, the wings of many insects, the 

 halteres of the Diptera, tympanic organs situated in various 

 parts of the body, primitive chordotonal organs, and possibly 

 structures of a special character in the antennae, are probably 

 organs of hearing, and these by no means include all the modi- 

 fications of a mechanism which is more or less probably 

 auditory. Many insects possess structures on one or more of 

 the abdominal segments, which are possibly auditory organs, 

 and are usually termed pygidia. The pygidium of the Fleas is 

 well know to microscopists, and some Neuroptera possess 

 similar organs. 



My attention was directed by Mr. R. T. Lewis to the large 

 pygidia of Notochrysa gigantea, and I found that the end 

 organs in these structures resemble those of the cupola of the 

 dipterous halter very closely. Though the want of fresh material 

 rendered the investigation extremely difficult, I saw enough to 

 suggest to me the probability that I had true chordotonal organs 

 before me. 



