On the Sound Organs of the Green Cicada. 175 



and do not confirm the newer theory of Landois. I read a 

 few notes on the subject before the Field Naturalists' Club 

 of Victoria soon after. In later seasons I have repeated and 

 extended the experiments. As attention has been called to 

 the subject lately by Professor Lloyd Morgan*, who from 

 examination of the corresponding species at the Cape of 

 Good Hope has also come to distrust Landois' explanation 

 of the process, I have thought it well to put on record an 

 account of our green cicada, in which the organs are con- 

 spicuous, and which can be obtained with the utmost freedom 

 at midsummer. 



As will be seen from the specimens and dissections, the 

 organs are situated in the first two segments of the 

 abdomen in the males, occupying a space about one-third of 

 the entire bulk of the animal. This fact alone shows the 

 importance of the structure to the insect in the struggle for 

 existence. 



By a comparison with the unmodified segments of the 

 female we find that the sound apparatus of the male has 

 been developed by a specialisation of the terga of the first 

 abdominal and the sterna of the last thoracic and first 

 abdominal segments, accompanied by a remarkable develop- 

 ment of the muscles of the trunk of the same two segments, 

 and a suppression of the muscles of the succeeding abdominal 

 segment. 



In the anterior membranous slope of the dorsal surface of 

 the first abdominal segment, facing the thorax, a pair of 

 elliptical, sclerous membranes are difierentiated, one on each 

 side. These are set obliquely to the long axis of the body, 

 are convex backwards and upwards, and are strengthened 

 with chitinous ridges running from the anterior and inner 

 to the posterior and outer angle. These are the rattle- 

 membranes, by the internal friction of which, of the ridges 

 on each other when in rapid vibration, the sound is 

 originated. These rattle-membranes are protected by a 

 corresponding pair of stout plates which project forwards 

 over them, from what is in the female insect a mere 

 transverse ridge of the abdominal tergum. 



The ventral modifications are no less remarkable. The 

 confronting surfaces of the metathorax and abdomen, in 

 close apposition in the female, diverge widely in the male, 



* Nature, Vol. 33, Feb. 18, 1886, p. 369 



