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 antenne, 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. 
