Powell. — On Stridulating Organs of Cicada. 287 



consisting of two cavities cov-erecl by scales. Hence the sound may truly be 

 called a voice. In the female tlie musical apparatus is present, but very much 

 less developed than in the male, and is never used for producing sound." 



As T have not access to Landois' original paper I am, of course, ignorant 

 of the details of his description, but unless the cicada which he describes 

 diifers essentially in the nature of its musical organs from those found in New 

 Zealand, and also from those described more or less correctly by other authors, 

 especially Reaumur (see Kirby and Sjoence's "Introduction," p. 501, seventh 

 edition, 1856), he is most certainly in error. 



The stridulating organs of the cicada (PL XYIII.) are constructed on a prin- 

 ciple which is, I believe, unique. In no other animal, as far as I am aware, are 

 vibrating membranes made use of for the purpose of producing sound, and in 

 this respect they possess a peculiar interest. In the male cicada on the upper 

 surface of the first ring of the abdomen on either side may be seen a semilunar 

 opening with convexity posterior, and on examining this opening with a 

 magnifying glass it will be seen to lead into a shallow cavity closed in by a 

 plicated horny membrane. If a live insect be caught and these membranes be 

 observed during the act of stridulation they will be seen to be vibrating 

 rapidly, synchronously with the beats of the shrill sound. On examining the 

 under surface of the insect an oval plate will be observed immediately behind 

 each posterior leg^ of considerable size, and quite free except anteriorly. On 

 snipping off these plates with a fine-pointed pair of scissors we expose on each 

 side a large triangular opening, the apices opposed to one another, and but 

 slightly separated ; each opening leads into a roof-shaped cavity of considerable 

 extent. Anteriorly this cavity is closed in by a fragile but opaque membrane 

 divided into two parts by a chelinous rib, the lower half is pure white and 

 marked with parallel creases, the upper half is yellow and tougher looking ; 

 posteriorly the cavity is closed by a large tense beautifully transparent 

 membrane, it is very delicate and shines with iridescent colours ; it is marked 

 dr in the illustration. If we now carefully cut the body through anteriorly 

 to the membranes here described, and to the stridulating membranes, by a 

 little careful dissection we shall expose the immediate agent of the production 

 of the sound, and see two thick yellow bundles of muscle inserted below 

 into the parietes of the abdomen at the junction of the cavitary membranes. 

 These muscular bundles diverge like the letter Y, a delicate aponeurosis is 

 given off from each muscle, w^hich seems to be lost on the rim of the 

 transparent membrane ; the muscle itself ends in a round tendon which is 

 inserted into the under surface of the stridulating membrane. This membrane 

 is highly elastic, and the sound is produced by the contraction of the mnscle 

 straightening out the plications of the membrane j this produces a click, and, 

 on the muscle relaxing, the membrane from its elasticity springs back with 



