490 JOTTINGS FROM BIOLOGICAL LABORATORY, SYDNEY UNIVERSITY. 



consideration of the small bulk of the insect and the great volume 

 of air that would be necessary in order to keep up the very loud 

 sound produced would be sufficient to shew. 



The structure of the sound-producing organs in this insect and 

 the mode of production of the sound were correctly described by 

 Reaumur. (1) Attention has recently been called to the subject by 

 Mr. C. Lloyd Morgan of University College, Bristol, who, in an 

 article in a recent number of " Nature," gives an account of some 

 researches of his on this subject published some years ago, but 

 apparently overlooked by recent authors of English Zoological 

 text-books. 



The sound is really produced by the bending of a stiff thin 

 chitinous membrane strengthened by stronger narrow ribs, which 

 is situated on the dorsal aspect of the first J abdominal segment- 

 The membrane is acted on indirectly by a powerful muscle — the 

 largest by far that the insect possesses — which springs from the 

 ventral side of the abdomen, and runs upwards and outwards 

 towards the dorsal surface. This muscle ends abruptly in a trans- 

 verse horny plate, from the centre of the upper surface of which 

 a tendon passes to become inserted into a part of the frame 

 supporting the membrane. 



The loud shrill note emitted by the insect is the result of a 

 quick succession of crackling sounds produced by the movement of 

 the stiff aiembrane with its horny ribs through the agency of the 

 muscle. Under ordinary circumstances the sounds follow one 

 another with sufficient quickness to produce a continuous note, 

 and this is effected, not by the contraction of the muscle as a 

 whole, but by the successive contraction of individual fasciculi, all 

 of which act on the horny plate, and thus the movements of the 

 muscle on the tendon during the production of the note resemble 

 these of the hammer-board of a piano when a number of the 

 keys are being struck in quick succession. (2) 



(1) See Pagenstecher's " Allgemeine Zoologie," III. Band, p. 143. 



(2) The tense membranous drums on the ventral surface of the abdomen 

 of the male Cicada, probably act as resonators, but their entire removal 

 seems very little to affect the loudness of the note. 



